1) offer a site license, where my customers can install my product on as many PCs as they want?
You can set however many activations you'd like for a product key. So if you want to set it to a very large number, you can do that.
2) if the answer to 1 is yes, could this be accomplished with one license key or would they need a license key for each installation?
1 key is fine.
3)use Delphi XE2, as my product was coded with Delphi XE2?