yeah they definitely need a heater they aren't goldfish. they can be kept with tankmates but i would keep one with tankmates in anything less than a 125 or 150g tank, for one by itself it would still need around 125g footprint to be comfy, these guys are more territorial than anything, so as long as he feels he has enough space he will most likely keep to himself, for more than one cichlid tankmate you would need more likely a 150-180g tank with larger being preferable, females get about a foot while males get about 14-16in with 18in being possible but unlikely. also i wouldnt reccomend feeder goldfish as they are very unhealthy, live insects are a much better choice if you want to feed live foods as treats