good choice! i have a 14 hgallon and wish id gotten the 29..anyway as for your stock list personally id ditch the peppermint and get two cleaner shrimp, i have 1 and he has the most personality out of my whole tank. ive heard firefish are quite timid so again my personal choice would be no but if you like it go for it. the cardinal is a suitable choice as well (im planning one as my next fish) ive been told they are happier in schools.
nassirus snails(clean sandbed)
Nerite snails(very good glass and rock cleaners)
maybe some ceriths(mine kinda suck but they help)
blue leg hermits (eat detritus, fun to watch. have extra shells )
the cleaner shrimps will help alot as well