Well done for asking questions first. But there is soooo much about rats I couldn’t put it in one message. That cage is a good size for a trio of rats, a trio is better than two as they are social animals and better dynamics. It’s good to give rats wheels, at least 15 inches big (silent spinner or tic tac are most popular) but it doesn’t mean that your rats will use it. I’ve used fitch in the past and liked it but I couldnt get it easily. Alternatively you can use cardboard squares or cardboard strips. Litter tray with pellets, I use breeder celect.
Do you know the age of the rat? Best to get two youngsters, at least 10 weeks old, up to about 5 months. Any older and you might have behavioural issues. But you can with any rats. You would need to introduce using the carrier method, found on this forum, I swear by it.
In your cage, take out shelves And put in ropes and flat hammocks. Once your group have integrated well and are used to you, then you can introduce tubes and hidey holes and houses. You also need to have a safe place for them to free range. I either block off my hall, use the spare room or people use the bathroom, so long as there are no cables or holes they can squeeze in to.
The other thing to consider is vet bills, and there will be some. Every rat I have had has been a rescue, sometimes I was at the vet weekly. However, more recently, my last visit was a month ago.
Good luck and I hope I haven’t put you off

Officially ratless. Groot, Star-lord, Yondu adopted by another rat lover.

To all those who have filled my heart, have fun at the bridge.