What a nice looking boy you have there! He is very handsome and I would be so proud to have such a great rooster. That is wonderful of you to take him in as you did. I know he is so grateful to have a home.
I do also want to warn you that Rhode Island Red roosters have a reputation for sometimes being very aggressive about guarding their ladies. Take away the ladies and there is nothing to guard, sometimes.
But every rooster is an INDIVIDUAL and he may keep being a wonderful pet for you. I do indeed caution you to not quite think of him as a pet that you can trust.
Never place your eyes near him (as in letting him sit on your shoulder and you turn to look at him), nor allow a child to be near him with you not around (and if it is a small child, don't even let the roo get near in my opinion) as roosters and small children don't mix too well due to the unpredicatability of the roosters.
You didn't mention if you have children, but I thought I'd mention it since you are new to chickens. Welcome to BYC!
and I hope you can get him a nice flock of at least 8-10 ladies to prevent bare backs (I have seen this happen before and there is raw/bleeding skin involved) as he will tread on them with his claws when he mates. I once only had 5 ladies with one roo and that was a major problem.
The easiest coop to maintain in my opinion is a shed coop. Sooooo easy to deal with and you can view the coop section on here to get ideas. You can get a regular shed and make some changes to it on the inside/pop door added, and there you go!
Or if you are very cost/time conscious right now, you can see that many have posted their ideas with free and recycled materials.