What is the typical workflow for UV unwrapping a realistic tank?

I am aiming for a realistic tank and so far it consist of multiple parts. In the tutorial you joined most of the models and unwrapped the tank in one texture (except for the treads). I used for a few models subdivision surface modifier and don't want to combine them (by the way should I actually avoid subdiv modifier?). In case of I  would use Substance, should I combine everything in one UV map?

I hope my question is clear. I just don't know how to progress now from the model.

Kind regards,