I'm playing it now too. My party is Zidane (Thief), Vivi (Black Mage), Garnet (White Mage), and Fabio (Warrior).
I'm about lvl 20 too, 3 hours of playtime, got the first crystal (although it's the second one in the menu, I skipped something?). It's been fun to play an old RPG I know nothing about. I wouldn't recognize an extra dungeon from the regular ones, and I think that's gonna be great.
OP, I plan to continue with FF2 GBA after I finish FF1 GBA. If you're going for it too, you might want to check this out:
http://www.romhacking.net/hacks/853/It's been reviewed as: "Final Fantasy II for Sane People". Might fix the things that make other people on this thread not like it.
(I don't know about the FF1 part of the mod, I'm playing without it because I found out about his after I started, but I'm definitely using it for my FF2 run).
Then I plan to tackle FF3 on PC, and hope my Snes Everdrive arrived from china by the time I go for 4-5-6 on SNES (all retranslated... 4 with this patch:
http://www.romhacking.net/hacks/2247/ , 5 with the only one that exists, and 6 with this
http://www.romhacking.net/hacks/2247/ which is based on the GBA retranslation).
I'm skipping 7-8-9 because I've played them already. Still, it's gonna be awhile, I don't play for more than an hour a day. I hope by the time I reach 10 it will be announced for PC so I can play that version.