Well its a hit or miss with the Morays, you might have got one that doesn't care about tank mates. For me to consider tank mates I'd want at least a 75, although I'm leaning towards a 125 if it's not going to remain species specific.
As far as brackish catfish go there's not much to choose from, and there's only one that's common in the hobby which is the Columbian (Silver-tip) shark. It's actually a full saltwater shark as an adult, sold as FW
in the stores. But they will get far too big for your tank and need to be kept in schools. I'd wait until you reach full strength saltwater and find a marine catfish. The first that comes to mind is the Coral catfish, solitary as an adult so you don't have to worry about keeping them in schools. Just make sure the salinity levels for them match first.
I'd also upgrade the tank before adding anyone else if you didn't already plan to.
As far as the feeders go, how long have you had your Moray? And how long have you left the feeders in the tank? I had mine for a few weeks with about a dozen or so feeders on the tank and he would just pick a few off here and there. Once he adjusted, and especially once I got my salinity risen, he became a lot more active and knocked the rest of them out.. pretty much over night. It's been 24/week since.