1) Read the FAQ (link in my sig titled "Thinking Abaut Hacking A Wii? Read This First").
2) You need a Wii that supports playing DVDs and something to play them with (WiiMC is my personal favourite). And yes, most should work.
3) Yes it's possible, use WiiMC.
4) It should look like SD:/apps/appname/<app contents>. Each emulator has a specific place it looks for ROMs. There's probably a guide the emulator(s) you want to use on here somewhere.
Finally, to completely softmod your Wii, use the Softmod Any Wii guide (again, link in my sig). It will set you up with everything you need.