>where to get roms
way back in the 56k / slow DSL days, I used to download individual titles from emuparadise. obviously that's gone down now. I got most of my fullsets over the past several years from archive.org and rutracker.
archive org is sort of a whack a mole game, as people will upload fullsets but they will get DCMAd, then another person will post etc. It's pretty great for old cartridge games, anything GBA or older you'll almost certainly find a fullset on there.
rutracker is pretty great for newer systems and disc-based sets. I got my PSX and Mega-CD fullsets from there within the past year. just search for "$systemname set", and there's lots of content.
The eye is pretty good for grabbing single roms here and there. I think you can script up a scraper with wget, but their collections aren't complete so it's not really worth it.
I've also used Vimm's lair and Edgeemulation for some stuff recently.
The hardest part about the fullsets is getting ~thousands of files unzipped and sorted them in some way that makes sense, is easily searchable, and doesn't have too many files in any one folder (some flashcarts have limitations on files per folder and don't accept zipped roms).