This is kind of late, but...
Most guinea pig cages have very spaced out bars, most adult rats can fit through a 1"x1" opening, so be very wary of bar spacing.
I detest tanks and aquariums, rats produce a very large amount of ammonia and it gathers on the tank walls, contaminating the rattie's air supply.
That, and where will you hang the toys?
There really is no 'taming' rats, they love human company no matter what. It just depends on what you want from a rat.
Males(if neutured) tend to be lazy, snuggly laprats. My boy loves sitting in my lap on his back to have his tummy scratched.
Girls are very active, and love games and toys. My two current girls live in a extremely large cage(a ferrret could live comfortably) with toys and ropes and hammocks but still get bored and love to come out and play with me.
girls, however, are extremely prone to tumors. Most are harmless, but some are fatal and painful for your rat. If you get a female, it's best to have her spayed to reduce the risk of tumors.
Hope you enjoy your new companions!
