working on a tank on my game. some questions.

hi.
im working o a top down tank project. my first question is should i build it whole in one part and rig it or wheels and canon and torret should be made on diffrent .fbx files and after that be added in mesh editor on ue4 to the main body? i want it to rotate free.i read tank artice on wiki page but i think it wasnt compelete and it wastn explained very well.

my next question is how can i apply physics to it most efectively? for example when tank hits a rock the tank start waving. if i define physics asset well, it works automaticaly or there are a lot of options there? im not much familiar in it.

my next question is how can i make it customizable? for example in one level i want to be a texture applied to it and next level another texture. and how to make proggresing abilities to my game? like make torret stronger or… add new gun? i know it is just working with variables but i dont know how to connect a trigger in level to other actors.