I have had rats on and off for over 20 years and have a friend who breeds and shows them.
You do need to have 2 or more together, as they can seem to be fine, but then pine away and die in severe cases, many people are lucky and one is ok, but there can be a big difference in the rats behaviour and wellbeing when they have a friend, they are also supposed to live longer with company.
Males are smellier, and can be a problem if kept in pairs. They can also be more aggressive as they get older.
The best thing to keep them on is the paper based cat litter, as sawdust and shavings aggravate rats lungs with the tiny particles, it can make them cough and actually cause long term health problems.They do love the torn up j cloth bedding stuff, it's really funny to watch them moving it around until it is just so.
You need to treat them like a small child really, give them lots of attention as soon as possible, things to keep them entertained as they are very intelligent and easily bored, and make sure there are no wires or cloth anywhere near them, as they really love to chew,lol.
As snowy girls said earlier they should not be housed in anything with a wire mesh bottom as they can get something called bumblefoot, which makes the bottom pads of their feet swell up and is really painful for them.
I found that other than a large glass fish tank, the best bet is a ferret or chinchilla cage, as they are made with strong teethed animals in mind. They also make accessories for these cages that you can add to stop boredom.
I used to have a lovely rat that lived in my pocket if I went out, and liked to ride around on my shoulder, under my jumper, and poke his head out to look around.They are so friendly if you give them enough time and attention.
My kids are trying to persuade me that we need some more, as it has been a couple of years since the last ones died and they miss having them around, but they are nearly 16 and 17 now, and rats live for a good 3 or 4 years, so I don't think it is fair whilst they don't know what they will be doing next.
Hope this helps, and I look forward to hearing about your new rats.