The ION board should be good enough to be used as an HD media player. The only thing it'll struggle with is newer games.
If you really want a power house, you should be able to keep the 9300 cool. I would mount the fan on the side of the heatsink and have the exhaust air ducted to outside the case. Then you won't have as much heat hanging around inside the case. I would plan on getting a dedicated GPU if you get the 9300, the onboard graphics are comparable to the ION and will really hold it back for gaming.
Unless you plan on dropping your NES PC often, I would just use hard drives. The SSD will be faster, but probably not noticeably.
The slim external drives are the same as laptop drives, so probably a good chance they'll be IDE. It shouldn't be too hard to find a SATA slim drive.
yeah i don't know why people would get the ion f-e when all it has is a pcie x16 express slots, the graphics may be better but your processor'll be holding you back.
when i do make a 9300 build (or whatever is best) i'll be putting a dedicated gpu and it'll be a minimum c2d if not a q2d, unless again, the future rapidly grows again.http://www.youtube.com/watch?v=pJMGAdpCLVg
^ shows how much a difference in ssd and hdd is but for that much improvement for that many dollars i'm starting to think it's one sided.
still deciding on the disc drive since if i were to sell this nes for a future nes build having a bluray player would help..