A few words of caution on firefish, they are big time jumpers, so a top of some kind is a must. They are also intolerant of their own kind in aquaria, so unless you get a bonded pr one will kill the others.
Other suggestions for a 45g include pink streak wrasse, midas blenny, stigmatura blenny, royal gramma, zebra dartfish, grammistes blenny, grammica goby, swales basslet, yellow head jawfish, watchman goby.