For the hardware, I'd recommend two things:
- Arcade Card Pro -- this will allow you to play every single CD based game out there (minus Altered Beast, in which you need a System 1.0 card due to a bug, but that's no big loss).
- Tennokoe bank card. Allows you to back up your memory, which fills up quickly, especially if you play RPGs.
Oh, and you don't really need the A/V output mod on the Turbo if you're going to put the CD Add-on, as the CD-ROM attachment has the a/v output built in. If you were going to mod it, you should probably just go other types of output, whether it'd be SVHS, SCART, component, etc.