Snakeheads are awesome, wish I could have one here in the U.S.
Lots of good choices for your tank size. Shoal of hujeta gars would be cool with a catfish on the bottom.
One thing I will say, is please don't feed "feeder goldfish" from the stores. These things are kept and bred in such bad conditions that they almost always carry some sort of disease or parasite. Can get your fish sick, and on top of that they are almost all fat and no nutrition, like eating doritos for us humans.
You can easily set up a 20-30 gallon with a pair of convict cichlids, as long as you have plenty of hide spots and a male and female, they will breed like clockwork every month or so. Then you can just feed your big tank the babies. And feed them frozen foods inbetween convict spawns.