If you want to build your cage out of grids I suggest getting a pair or trio or boys. The females can usually slip through. A good way to determine cage size is to use the (broken link removed).
I feed Mazuri lab block and Nutro Natural Lite dog food (it has much less protien) mixed. 1 part dog food to 5 parts lab block.
The best block is Harlan Teklab. You can buy it at (broken link removed), although shipping to Canada would be quite a bit.
I feed my boys lettuce, jimica, tomatos, carrots, cucumber, etc. for veggies.
They also get whole grain organic oatmeal with soy milk. A little goat cheese, maybe some whole wheat crackers, a little whole grain bread with some olive oil for their coat once a week, couscous, and whole grain rotini pasta (their FAVORITE).
For junk food they get Yogies (friut flavored) a piece of a PB&J sandwich, a
little piece of dark chocolate, stuff like that.
The rat forum I like the most (and is the most pro-adoption) is (broken link removed)
PM me if you have any questions.