I wouldn't hazard an ID off those pics. You need a good headshot and dorsal fin erect, but I suspect it's a female.
54L will do 2 - 5 of them of as long as you can keep it cool. A desk fan pointing at the water is a good trick, and keeping it in the coolest room. I'll have to turn my chiller and pump on very soon, my 430L is already getting upto 20.5 deg on warm days.
as above for food, common and Cran's tend to take to commercial food better than redfins that I've had. small worms, snails, flies, moths, backswimmers, mosquito larvae, etc will all vanish. Try nutrafin discus max for a good commercial food that all my bullies and small galaxiids have loved.