there is no limits for this thing.u can put it anywhere u want.but i think TOS say dont put ad on welcome page and thank you page.i donno if its right
unlimited, but you should use channels to let you distinguish between what clicks came from which sites.
just be careful when putting ads on more then one site/blog. if any one of the site is against TOS and if you get ur account banned then all sites would be without any revenue source. like they say.. better not but all ur eggs in one basket
Once you start making a lot of money with AdSense its a good idea to start new corporations to split your AdSense earning into different accounts. This protects each one from being banned or smart priced or whatever. I think it was shoemoney who said every time he had a site that got to arounf $10,000 a month in AdSense he would create a new corporation for it and create a new AdSense account for the corporation.
I guess it is not really worth it when earning 10$ a month ;-) What are the chances of being kicked off? I see alot of posts here of angry people being kicked off for no reason?
From a legal standpoint your corporation is as distinct from you as if it had a separate body. It has it's own tax number, files its own tax returns, keeps its own books etc. That's the whole point of a corporation.