More Pet Rat Questions and Help?

I got two pet rats from the local animal shelter the other day. I got Oreo the day before Snickers because I didn’t realize that it is best to get more than one. They are both about six weeks old and litter mates. Yesterday I noticed that they were wrestling. They kept rolling around on top of each other and making soft squeaking noises. I can’t tell if their fighting or playing. They chase each other around and tackle each other. Last night they kept wrestling for like an hour I would get them to stop sit down and they would do it again. Is it serious? I can’t tell. I take them out of the cage everyday and hold them and I haven’t seen any scabbing or bleeding. Is this normal? Can it lead to something more serious? Please help. Also what do you think of this cage http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=23204 the one they’re in now is kind of small for the both of them but I will be getting a new one soon I'm leaning towards this one. But is ¾” bar spacing to far apart for them. They are kind of chubby the love to eat. Also I’ve found that they LOVE watermelon. (I pick the seeds out) and corn on the cob. Black oil sun flower seeds, seedless grapes, and even tomato. Is this ok for them?