I want to build a PC for emulation

While I intend to use it to emulate other consoles too, Dolphin is the most resource-intesive. I've done a bit of research, but I still don't know all I want to know. I want to be able to run most Gamecube games, or all of them, if at all possible. Wii doesn't interest me as much.

1. Will a dedicated sound card (as opposed to the motherboard's onboard audio) diminish problems with DSP and "Frame Limit @Audio"? Do these even still exist?
2. Video: The consensus seems to be the best AMD I can get, is that right? (Also, SLI doesn't work with Dolphin)
3. Processor: I've found this spreadsheet floating around the forum: https://docs.google.com/spreadsheet/ccc?...Fa1E#gid=0 Is it up to date, can I trust it? Are there better processors?
4. RAM: Is there a point where one can have "too much" RAM for Dolphin (As in, there's no use for all that RAM, and I'm just wasting money)
5. Hard Drive: Do you think I can use a 7200 RPM "normal" HD, or do you believe the loading times would be annoying and I should instead get an SSD?
7. While that question is not quite hardware, what is the state of Dolphin on Linux? Is it as good as the Windows builds? Any caveats?
8. Any hints? Something I didn't cover?