What kind of filtration do you have? How old is the tank? Do you have any live rock or just stones? Porcupine puffers have very good personalities, but they produce alot of waste, thus need a system(tankmates, filtration, etc) that can handle it. Also, porcs like to feed on shrimps, snails, and crabs, so your cleanup crew would slowly decline, but if you have no problem replacing them, then it really isn't an issue. An 100g would probably work for a long time(for a porcupine puffer), possibly for life, but many of them get to be very very large and require bigger tanks. Also, are you trying to make a community or agressive tank? The huma huma can pose a problem. Does he pick on your sailfin?
Flashy, active fish to consider:
School of green chromis
Flame Angel
Coral Beauty angel
purple tang(caution with sailfin)
yellow tang(caution with sailfin)
hippo tang(peaceful/ beautiful fish, but can grow large)
with the exception of the chromis, all of the above listed fish are pretty sensative and need a established/stable tank.