Currently housing a bowfin (16"+/-), yellow bullhead (16"), lmb (8") and bluegill (6") in the 300 gal part of our native tank. No aggression issues, but the sunny and lmb get the bulk of the food. I takes the bowfin a minute or two after the first food hits the water to get going. Never see the bullhead until the tank is dark. SOme of the plants are natives, but not all. Been trying to collect different types of local bog and aquatic plants, but there is little diversity here.
Tried 4 florida gar in this tank in the past (before the bass and bluegill) and had no luck with that setup at all. The gar were consistently outcompeted for food by the bullhead and bowfin, who were only slightly larger than the gar. That meant I needed to overfeed the bow and bullhead every time i fed the gar. The gar needed to eat more often than I could accomodate in that setup, so I moved them. They also seemed stressed all the time. The gar are doing much better in a small pond.
Look into black crappie and fliers. Also chubsuckers are a good bet. Avoid shiners, even big golden shiners eventually get eaten.
Also consider fish too small to be bothered by the gar. We had Heterandria formosa, mosquitofish, fundulus killies, even baby bluegill and pygmy sunfish living with the gar, bowfin and bullhead. They disappeared within a week of the lmb going in the tank.
Don't forget to quarrantine and treat for parasites!
Oliver