Firstly, welcome to sSnakeSs.com!
Reasons for soaking can include: low humidity, insecurity, ticks/mites, high temperature (although this one never makes sense in my mind since the water would be the same temperature? but I've seen it countless times so I can't argue it). What is your setup like?
As for cage size, most adult females can be kept in a minimum of 4x2x1 (if you want to decorate it will need to be larger). I find 2' height to be overkill and wasted by the snake, unless you are building a shelf for your snake (which it may or may not use). Of course, as mentioned above, if you can afford to go bigger then all the power to ya