I've had pet rats a few times in my life, and I absolutely love them! They're really sweet, intelligent, social animals. If I didn't have cats right now, I'd have rats again
The most important things I can tell you about their care is:
1) They're very social. Buy at least two so they can interact and keep each other company.
2) Let them exercise. I let my rats out daily for about 30-45 minutes and supervised them. They'll chew on cords and wires, so keep a close eye on them!
3) Feed them fresh fruits and veggies! On top of their daily dry mix, you can feed them small bits of fresh carrots, lettuce, apple, etc. They're very healthy little creatures.
My little ones also LOVED having a hanging hammock in their cage. They snuggled in it all the time.
PM me if you have any other questions.