The problem that my friend who has pet rats fell into is the situation of having two rats, and then one of them dies, and you get another rat so your remaining rat has a companion (might sound silly to non-rat owners but they're social enough animals that that's a concern), and of course your new rat outlives your original rat, so you need to get a companion for that one, and you enter into the "rat cycle".
Yeah, I'm keeping in mind the social dynamics of the cage. We have three rats. As soon as one of them dies, I intend to get two baby rats. Then I'll likely get a third baby sometime after that, depending on when the other older rats die off.
The real problem is suppressing the urge to adopt new rats because you found a really sweet one at the pet store. Our litter trays are full enough with our three girls. If we get more, then that's even more litter to empty.