I've currently got a very small tank (more like a bowl) for 2 cold water fish (a shubunkin goldfish and a comet goldfish) and i'm intending to buy a large tank for some tropical goldfish and a couple of crabs. I was wondering if I could put the two cold water goldfish in this tank, since it will be heated for the tropical fish and the crabs? Will they survive in the conditions of a tropical tank? Also, will the crabs eat or kill my goldfish?! Or the tropical fish? Help with any of these matters will be much appreciated!!

PS. Is there anything apart from a filter and a heater that I will need for my tropical tank?