On ur mark, get set, Sherman!

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.

what about an undercoat? Are they silver of something like that coming off the assembly lines? When they get scratched and scraped, what showed through?

I'm not an expert on Shermans but a similar thread a while back indicated that they didn't have an underlying primer coat, just the OD. So if scratched, it would show metal underneath. Most use a shade of gray to represent this as opposed to silver since bare metal wouldn't stay shiny very long at all under exposed conditions. HTH.

I've seen the underlying color as black. That may be rust or just a trick of lighting. I wouldn't go too shiney.

I would not think the bare metal on a tank would be silver like an aluminum aircraft. Maybe darker like an old iron pot or you might look at the color of steel and/or angle iron at a welding shop. This is what I go by, although it's just a guess. Good luck!