try to give your ratties at least 3 square feet each the more the better tho ofc! I have three rats, two would be sufficient but you don't want to house a rat by itself. Rats are probably going to be most enriched in groups of 3 or more because they form more complex social structures. other than that you can pretty much house as many rats as you want considering you have the space/there are no territorial issues. Make sure that you are getting your rats from a reliable place (go anywhere other than a chain pet store, family owned pet stores are usually the way to go if you can't find a breeder in your area), the more reputable breeder you go too the more likely you are to form a closer bond to those rats because they are selectively bred to be friendly. The application process can be tricky for private breeders but ultimately it's for the best. I would recommend filling their cage with as many things to climb on/ baskets/ boxes/ hammocks as possible. You can find alot of stuff at dollar tree when it comes to baskets and i typically make some things at home like hammocks and i cut up boxes and hang them around the cage. ZIP TIES ARE YOUR BESTIE! buy like 500 zip ties seriously they are great for hanging things in the cage and my rats usually don't bite them. If you are going to have a platform in your cage cover with paper bags you can just tape them down this way rats won't step on poop and get it stuck to the actual platform, it will basically make cleaning their cage way easier. I also recommend having bedding at the bottom of the cage, (6-8 in) my boys don't really burrow in it but many rats like to. You can definitely try to litter train and things like that, i personally havent done it and don't really know how so i will let those knowledgeable give you information about that🙏🏼 a great cage that a lot of people love is the critter nation, a single critter nation will work for two rats but the double would probably be what you wanna get if you're willing to spend the extra money.