Pet Rat Help and Questions?

Ok, so I just got a pet rat today from the local animal shelter. It is a 5 week old male. He did have a brother with him in the cage but I only got one. Should I go back and get the other? The one I got seems pretty calm and the other one did seem more active. would they fight? they were in the same cage and they didn't fight or anything. Also I named him Oreo since he is black and white. I have been trying to come up for names for the other one in case I do go back and get the other one tomorrow. I was looking at names to go with Oreo and I came up with Snickers. Any other suggestions? Also the cage is big enough for another. There would be plenty of food and room. Thanks in advance.