While I do think the form factor will be similar to the Infuse, I highly doubt Infuse cases will fit. Hole placement and size have to be perfect, and I'd have to think there will be subtle differences.
Probably not. The phone will be thicker here in the states than the international ones. It's the 4G / LTE modems that will be put into the Galaxy S 2 for the US carriers.
Yes, the Infuse cases will fit, however. The only difference is that the micophone on the epic touch has been moved slightly to the left so you will have to poke a new hole in order to speak on the phone.
Just got my TPU Matte Black case from Amazon for less than $10 and it's perfect!!! Slimmer than I expected and the quality surprised me too. I highly recommend it!