
I've had rats for about the last 9 years now - currently we have Susan and Holly, and Leonard and Sheldon (separate cages!).
I would always recommend more than one, two or three is a good number and if you have one now you would be best placed getting two young boys and introducing them - cage size guidelines do vary and obviously they do need enough space BUT, boys require in my experience quite a bit less space than girls, they are a lot more idle (and because of this make the better, more handleable pet).
Most fancy rat people feed a mixture rather than one standard product - usually a mixture of a good quality dry dog food, a rodent food (a high quality rabbit muesli is often good, not one that contains alfalfa though, it won't do any harm, its just wasted as they won't eat it) and then dry pasta.
Usually thats fed as the basic daily food - mine hav etheir bowls filled up each morning, and then they get fresh food, human left overs etc in the evening. Mine eat most of our left overs, nothing too high in salt or fat or sugar, but theres v little they don't like.
They SHOULD have some meat in their diet (hence the dog food element of the mixed food), they CAN be given cooked bones as they gnaw so splintering isn't an issue.
Its easy to get sucked into buying expensive hammocks etc (and there are some REALLY nice ones around, look at Fuzzbutts.co.uk) but they will be just as happy with hammocks made from old teatowels, cut off legs of jeans etc.
Finally - never use sawdust, if you haven't been told that already. Paper cat litter is an ideal substrate and some of the horse beddings work well too (aubiose is good i think) though these are only really practical if you have a lot of rats!