Rats are excellent pets, I have loads of them!!!
You do need to get a pair or trio, rats are very sociable animals and it is really quite cruel to keep one alone, it can also mean they become insecure and viscious.
Try www.equinecanincefeline.co.uk for cages. The 'Jenny' is a good size and reasonably priced, although some people find it a pain to clean/access a pain. I have three of them and love them. The bigger the cage the better though. I also have the Furet Tower, which is great, but you might feel it is too big for two rats.
Foodwise, I feed a mixture of pellet free rabbit food, dog kibble and then add low sugar breakfast cereals, brown rice, crushed up ryvitas, rice cakes anda few other bits, I vary it each time. If you don't want to go to such trouble, pellet free rabbit food with approx 10% dog food added would be good. (James Wellbelovedor similar dog food is good) Commercial rat food is't at all great, although some of the muselis are better than the pellets. Rats get bored easily. They should also have fresh food everyday or other day. Fruit and veg, especially kale, boiled eggs, chicken carcasses, fish etc.
Rats really need time out of their cage every day so they don't get bored. Quite a few owners set up a 'playpen' for them with toys in that they don't have in their cages. They are really very intelligent and will soon learn to come to call and tricks if you teach them.
As for breeds, there aren't any, they are all 'Fancy Rats' but you do get different varieties, which are basically colours/patterns. You can find details of them here www.hawthornrats.co.uk/varieties.
A breeder is the best source for rats. They will breed for health, longevity and temprement and babies will be well handled and socialised. You will have to sign a homing contract and agree to return the rats if at any time you can no longer keep them. If you go on the NFRS website, they will email you a list of registered breeders.
If you want to know anything else, just ask.