the Japanese anti-China faction was the dominant faction. the Japanese had a long-term plan of invading China. but decisions are shaped by events. events will shape decisions.
if China became stronger, Japan will surely reconsider the wisdom of the invasion. from 1927-1937, China was developing and modernizing very fast. a great deal had been done toward improving the economy, military and living conditions. the Japanese were worried about it. Dr.Arthur.N.Young, WW2 finacial advisor to ROC said that the Japanese had reached the conclusion in 1937 that it was now or never.
things will develop, change or happen depending on circumstances. therefore the cause of the China-Japan war should be considered against an all-inclusive background.
Since you agree that the anti-China faction was the dominant faction and Japan had been planning to invade China for a long time, Japan would invade China with or without Lugouqiao 7/7 incident. And you also said that the Japanese had concluded in 1937 that it was now or never. So if it wasn't 7/7, it would be close to that date.
most Chinese historians will agree that 7/7 were started by Japanese junior officers of Major rank and below. it was not planned by the Japanese Tianjin garrison. Nanking and Tokyo simply went along with the flow of the situation and declared war on each other.
according to KMT general Li Zongren. at the onset of 7/8. the Japanese moved its troops too slowly to the conflict area. the Japanese redeployed troops from northeast China, Manchuria and Korea bit by bit. Japanese had 20 standing Shidans ( Army Division ) in Japan at 1937. they could mobilize to 50 Shidans. they could quickly deploy 30 Shidans to China from two directions: North and South simultaneously. but the Japanese didn’t do it. this suggested that the Japanese were not that prepared for war. the Japanese rushed the war a little.
the CCP never planned for that much. it could be a local war, a region war or a short war. they simply wanted to embroil the Kuomintang into a war with the Japanese. to divert the KMT focus from the Communist to the Japanese.
it would be foolish for the CCP to sit idle and waited for annihilation. it would only be a matter of time before Chiang Kai Shek relaunched military operations toward Yan’an. the CCP took its risks and benefited greatly from the war. there was also the Soviet factor in it. the Japanese and the Russian reached a secret consensus that the Japanese troops would not invade Yan’an. the CCP would later establish friendly contacts with the Japanese Nanking HQ on its own without the Russian knowledge.
You said the CCP "did not plan for that much" and they intended 7/7 to be a local war to embroil the KMT in fighting with the Japs. Meaning they didn't think it would escalate to the full blown war. That's quite a big risk to take. Also, if the KMT General had acceded to the Japs request to let some Jap troops to search the missing soldier, the "local" war might have been averted and the CCP ploy would come to naught.
during the late 1920s to 1937, Li Zongren regularly entertained Japanese guests from the military, government, business and educational groups. according to Li. there was one group of Japanese ( one was Takaji Wachi ) who were very anti-Russian. against the Japanese long term invasion plans of China. they had this opinion that Russia would eventually invade Japan one day. Manchuria and Inner Mongolia would be the base to launch an attack. if the Chinese couldn’t defend its own provinces from the Russians. the Japanese had to take over these lands to make it a buffer against Soviet aggressions. Li described these point of view as totally absurd.
my point is there were different Japanese opinions with regards to the Japanese long term invasion plans of China.
the CCP sabotage operations of Japanese business interest and killing of Japanese citizens would sow the seeds of the war. to explain it and 7/7 will be too long.
the CCP sabotage operations in mostly Manchuria and North China from 1931-1937 were very complicated and different to understand. i mentioned earlier. i don't really understand it fully. to put it simply and short. the results of those actions weakened the position of the Japanese moderates in the government and military who preferred peace with China. the influential Business group ( the large corporations ) who had massive interest in China threw their support behind the War faction. the War faction eventually won control of the government and directed the expansionist plans toward China.
regarding 7/7. there were no direct evidences. but there were circumstantial and corroborating evidences that pointed to a CCP conspiracy in 7/7. it was a long story too. maybe i will write a bit on it later.
the Chinese Communist avaded the Japanese invaders for close to 8 years and rarely faught a decent battle. fact is stranger than faction. actually. the Japanese and the CCP troops lived side by side in peace. a Chinese newpaper reported, in 1941, Mao Zedong went to meet Okamura Yasuji in Nanking. ( i doubt it ) in 1943, Pan Hannian as a representative of Mao went to meet Wang Jingwei in Nanking. in June 1945, Yan’an sent New 4th Army staff officer Yang Fan to Nanking to discuss a CCP-Japanese alliance against the Chinese Nationalists.
http://blog.sina.com.cn/s/blog_af5c8fd601015zv6.html
Guo Rugui wrote this book - the history of the Sino-Japanese war ( 中国抗日战争正面战场作战记 ). the sources were from the Chinese Historical Archives at Nanjing today. stolen KMT archives. perhaps, Guo toward the end of his life finally found back his conscience and wrote this book to honor the bravery of the millions of Kuomintang soldiers and generals. Guo implied that the Nationalist fought 95% of the battles during the war. maybe, that was Guo way of saying sorry to his former KMT comrades who he betrayed and sent them to their death during the civil war 1945-1949.
http://baike.baidu.com/view/1610510.htm
As stated earlier, I am also of the view that the KMT fought the Japanese more. Taiwan Ma Ying Jiu recently asked China to recognize the truth that it was the KMT who fought the Japs. But we have to understand that the KMT and CCP were also at war with each other at that time, and that the KMT was in power and had the upper hand. If the CCP attacked the Japs, they would be exposing themselves to the KMT. Also, according to Sun Tzu Art of War, if your army is slightly less powerful than your enemy, you wait and watch but do not attack (your "living side by side in peace with the Japanese").
But it is a fact that the CCP did fight the Japanese. And they could only openly do that after forcing the KMT into a truce via the Xian incident.
You are wise to doubt the report in the Chinese newspaper that Mao went to Beijing to meet the Japanese general - because the newspaper was probably a KMT propaganda. It is not impossible that there were some communication between the CCP and Japanese and even talk on corporation against the KMT. But it could all be a ploy: the CCP trying to get more information about the Japanese and KMT. Surely, the CCP knew that enmity the Chinese people had for the Japanese with the unfair treaty still fresh in the minds. The CCP would also know that they would have an even tougher time getting rid of the Japanese troops after the defeat of KMT. It's not necessary to read too much into these communication between the CCP and Japanese. While it is not inconceivable that out of desperation for its own survival, the CCP could really reach out to the Japanese, we need at least some circumstantial evidence before making such speculation.
Also, before one accuses the CCP of being a traitor, let's remember that KMT Chiang Kai Shek had considered the CCP a greater threat than the Japanese (which he repeatedly made concessions to before the war). It is sad but true that if the KMT and CCP had united to fight the Japanese earlier, the Japanese probably wouldn't have been able to commit all those atrocities against the Chinese people. The blame for this should be shared between the KMT and CCP. I think a less power-hungry KMT leader like Sun Yat Sen might've made peace with the CCP to fight the Japanese.
Li ZongRen was right to reject the Japanese suggestion of grabbing Chinese land to be used as buffer against the Russians as absurd. Any fool would know that the Japs were trying to grab a piece of China here.
Now, your point about "the CCP operations against Japanese interests and killing of Japanese mainly in Manchuria sowing the seeds of the war by weakening the moderates in Japan" is just an inconsequential "IF". First, since the Unequal Treaty which seceded many Chinese territories to Japan, there had been operations against Japanese interests in China (whether by CCP or others) because many Chinese were against the Japanese occupation of their territories. Even if the CCP was the main saboteur of Japanese interests, it was just carrying out the will of the Chinese people - while the KMT at there time was making a lot of concessions to the Japanese. Second, since the Meiji era, the Japanese far right had taken over Japanese politics and had planned to take over China. Sure, as you said, "Japanese invasion of China was certainly not a definite". Of course, nothing is cast is stone - but the plan was there all along, and the moderates didn't really have a chance.
Why you are so fond of saying things like "Japanese invasion of China was certainly not a definite.", "things will develop, change or happen depending on circumstances. the cause of the China-Japan war should be considered against an all-inclusive background. " and that there are different opinions in Japan on attacking China ?
Of course, there would always be some dissent, just like there were some Germans who didn't like what Hitler was doing. Of course, things could change and the Japan might not have attacked China. There is always a good and bad side in every man, just like in every country.
A rapist preparing to rape a woman could have a side in him telling him that it was wrong to rape. But his bad side prevailed and he proceeded to rape her. And then you come out to tell the world that the rape wouldn't have happened if the rapist had listened to his conscience. Worst, you even suggest that the victim might be "indirectly responsible" because she did some things in the past which "sowed the seeds" of the rape.
Oh yes the US needs to attack every country in every region before you will admit it has aggressive policies. 
