I say Home Premium. You get almost all the goods, Media Center and all that. But you dont have to pay the hefty price. There is only 3 Ultimate Extras. Not worth that kind of Money in my opinon.
Depends. Check the software sites that you run to see if the versions they have run on 64 Bit. Also check your games and all that too. Might have to patch a few of them to make sure they work right. Not all apps work on 64 Bit and you would have to find a replacement.
No. If the app is not supported then it wouldnt even install. If 64 bIt is supported but the application is not 64 Bit then it emulates 32 Bit. But only then.