I said Saturn down. I have a PS2 and a Wii, no need to emulate either of them. Just now I found a mini-ITX board and CPU combo that comfortably run anything SSF can throw at it for about $130. Add a case, a psu, and a $100 gfx card, and I think it'd do fine, all for around $300. If I pick the right components and maybe get a good deal, I could probably emulate the dreamcast too.
I don't see why not. The main thing that matters is the hard drive keys. Also, I forgot to mention this before, but not only is the Xbox 1 a very capable multimedia and emulator console (aside from Dreamcast and Saturn anyway), you can actually get one for about $40 these days at thrift stores. That's how I got mine, and almost every Goodwill or Value Village I've been to since has had at least one for $40-$50
I had no idea the xbox 1 emulators were still being worked on. I'll have to buy a new controller and try them out sometime. Last game I tried on the PSX emu a few years back was parappa, and the timing was all off making it unplayable.