if your getting into tg-16/PCE i would suggest getting a region modded Duo-R. there not really very expensive and if you get it region modded you can play US and JP HU cards as well as the CD games without worrying about the cards, except for the arcade card. though if you already have a tg-16 and a cd attachment i guess that may be wasteful.

you mentioned Neo-Geo. if you want to get into that but are not sure about liking it. go the MVS route. it may be a little more expensive but in the long run with games you save a ton.