new here and have some questions

Regarding #2, I think mfvitools can turn a mml file into FF6 raw hex, or at least insert the song in the ROM. If you ever put a song on the wiki, you'll need the FF6 raw music data, the 32 bytes samples file and a SPC file you can generate with an emulator (like snes9x or zsnes) when the song play in-game.

Regarding #3, I think there's a tool in the mfvitools repository called insertmfvi that allows you to insert samples in the game, at least that is what emberling use. Prior to this it was done manually by relocating/expanding the samples pointers/adsr/loop point/pitch blocks, making a few ASM changes and adding samples. There are samples of other Squaresoft games here but some don't have the correct pitch value to be usable in FF6.

Note that I'm not a music hacker so I might got some stuff wrong lol