300 gallons is a nice sized tank for fronts. But they will eat leleupi and brichardi. It's not a matter of if, but when. Large comps would do well with the fronts. And you can put some synodontis catfish in there as well. As far as what type of fronts, that's up to you. My personal favorite is Cyphotilapia gibberosa (Kapampa). Good luck with the tank.