New hamster what do I need.

[Mollysfriends]

Hi my sister brought a hamster which was about to meet a sticky end. The shop said it was a roborvoski and as I had spare cages I was asked to look after him. However I think he is a Campbell's dwarf hamster he looks bigger as has a stripe down his back and has red eyes. He is possibly platinum I don't know much about them so can anyone tell me what they should/shouldn't eat(Can they eat fruit)? And whether they need climbing things. Also what size cage. I have him in a homemade cage that is 30 inches long 12 wide and 18 deep. Is this ok or does he need bigger/wider.