Welcome to the darkside! Depending on the kit you've got, the level of interior can vary from non-existent to fairly substantial.
As for the order of the build, that all depends. As a general rule of thumb most people assemble the hull and details minus the tools along with the turret and the running gear (suspension and parts for the tracks), paint, then add the tracks and markings. Lots of variation out there on methods though and there isn't one "correct" way to build armor since each kit has quirks of its own.
My recommendation is do what you do with AC, study the diagrams and parts prior to assembly and do it as you need to for accomodation of detailing and painting. Good luck and don't be afraid to ask questions here as you go along, we all remember our first foray into the darkside of treadheaddom.