water temp for optimal growth/health would be around 27-28degC. gravel doesn't to much to the growth of the gar, but darker gravel gives them more contrast in their colours. food wise gars are not that picky. but i'll steer clear of goldfish feeders, for they're rich in fat and have backbones, along with a vitamin B destroying enzyme.
as for plants, how big is the gar? and what size tank is he held in?
--a final note, gars do not generally do well with bass.