Even docile species can be temperamental their whole lives. So while you may get some that will calm down once they're adults, that doesn't always mean they will so take all that with a grain of salt.

I look at it this way if you were to get an aggressive one that would be like that its whole life would you still want it? If not then I wouldn't recommend getting one, if so then I don't see a problem.

Rat snakes can climb and I've had them before so I can attest to this from experience but this doesn't mean you have to provide climbing spaces. A terrestrial cage would be fine, just make sure to provide some hides. They can be elaborate or simple as far as setup goes so it's more or less how difficult you want to make it on yourself.

Also keep in mind that I've never had a Red tailed rat but I've had rat snakes in the past so I'm giving you my general information with my experiences with them.