If you have more than one, they'll keep their disputes amongst themselves mostly, but kept only with other species, expect them to push other fish around. They have mood swings (can be peaceful, can be cranky).
I keep mine with CA/SA cichlids and polys, with no issues. The GG's mainly have their spats when lights are off, evening and early morning (you can hear a splash here and there) with an occasional ripped fin, but they heal fast and well.
Variety is key in any fishes diet, all of my fish eat the following through out the day: hikari cichlid gold, tetramin color extreme granules, tetramin flake, spirulina discs, shrimp pellets, frozen krill, freeze dried plankton, and lettuce.
Their treats are night crawlers, and ghost shrimp.