My rats live in same-sex groups of two to six except in rare circumstances, in cages which give them plenty of space to live and play. I make a commitment to give each rat individual attention every day, typically with each cage of rats coming out for at least half an hour with me each day in a rat-safe play area with toys to keep them happy. This also serves to limit the number of rats I keep, as obviously there are a limited number of half hours in every evening. I use shredded card cage substrate; an economical and less dusty alternative to softwood shavings which avoids the possible health risks of exposure to wood dust and phenols in shavings. Cages are cleaned once a week, with spot cleaning inbetween where needed.
I feed the a home made mix composed of mixed straights (grains), a small amount of high-grade dog kibble to raise the protein level slightly, a few additions of human cereal to add interest, garlic and seaweed powder, plus plenty of green leaf vegetables (occasionally with added olive oil), other vegetables, some fruit and the occasional left overs from our own meals.
I hold my own vet fund to self insure against the expense of illness, and find that putting away 1 pound per week per rat gives me a good cushion against vet costs.