I would consider the cage you bought to be a temporary one -- for them to be healthy and happy, they're really going to need more space than that. At the very least you'll have to clean it twice a week, because the ammonia from their urine will build up quickly in a glass cage and it will make them sick if you don't keep on top of it.
This is a good site -- http://www.quite.co.uk/rats/ -- it's British so some of the terminology might be a little quirky, but a Harry Potter fan shouldn't mind.
OP, I used to raise fancy hooded rats. They are intelligent, friendly pets. I second the idea that you choose another option for their permanent home. They become quite large and need lots of spade. We made our own cage. It consisted of a plastic kiddie pool, with chicken wire set inside it, about 4 feet high. The beauty was that they could climb it, and the fumes could "escape." At the top I put a hammock that they loved to sleep in. Toys/things made for ferrets are perfect for rats.
I didn't have cats when I had the rats (Franklin and his son, Peyton). I had a dog. They were in no danger from her; more than once when they escaped (be warned: they are escape artists!) she'd pick them up gently in her mouth, intending no harm. Cats, I'm not so sure. I wouldn't mix rats with the cats I have now.
Rats are social and intelligent and need lots
of attention. They also have respiratory issues. The biggest reason I got out of raising them was due to the fact that I got tired of losing them.
And, IMO, the male rats were much nicer than the female rats. The male rats will "mark" you with a bit of urine at first. I know that sounds gross but if you're an animal lover like I am it's a small price to pay.
And another warning: never leave Halloween or Easter candy around unattended. Ask me how I know.