nygel!, ok help me out with this plz. in your last pic, whta is it right under your firefish's head? i have about 3 of those that randomly appeared on my liverock one day...
and i'd say 2 would be completely fine in your tank. i plann on a lawnmower, 2 firefish, and 2 cardinals in my 30.
they are small fish, and will do fine in your 40, and you can go with 2 or 3... i'd recomend 2, incase they mate the third one will have problems with the pair.