Goonches are not active swimmers so they don't need a lot of room to swim. How big yours is now? Kept mine at 4-8" in a 40g. From 8-15" had him in the 100g. Its currently in my 300g at 18" but I'd could have kept him in the 100 only moved him cause I needed to keep some other fish in my 100 that he'd eat.
Any fish to big to swallow could be potential tank mates.
How big that's yet to be explored. There are a bunch of us who have em will see just how big we can grow them in our tanks
http://www.monsterfishkeepers.com/forums/showthread.php?526963-Show-me-your-goonch!