Get 1-3 Panda Corydoras Catfish, 1-2 spotted Rubber Plecos( they stay small) and then 8-10 Longfin Serpae Tetra. Or, several botia or yoyos. 40g is gonna kinda limit you to smallish fish...a couple Green Terrors, not considered very aggresive and they have personality. Salveni are cool...little aggresive.