You can put it on as many sites as you want.. it's better if you use channels to track which sites are doin better.
Of course you can. Most AdSense publishers have a few sites if not a few dozens. Don't forget to read the TOS to avoid any problems in the future.
Yep, as many as you want. I have mine on about a dozen sites of my own and at least that many Revenue Sharing sites (similar to this one).
Like others said, you can, BUT it can be tricky. If you earn well with adsense, well enough to start another site with adsense ads on it, then you can find yourself actually in situation where you earn less. Why? Because of Adsense smart pricing. If it turns out that your new site is not converting to good, then Google will "smart price" your account NOT the website that converts bad.
That used to be the case. However, there's mounting evidence that they now do it on a per site or maybe even per channel basis. No one outside of Google knows for sure, but that's how it's looking. Therefore, it's wise to always create and use channels, just in case that is where the smart pricing filter hits.
you can use your adsense code on unlimited web sites (if the content is not against the adsense tos) . i also suggest you to create channels to track your earing on different web sites