imho the wheels are too flat right now also i seems as if the back wheels are separate objects, you could easily save a few tris there by making them 1 object with just an indent in the middle. maybe try something like this: (the backs on this are flat like yours because they're not seen that often)
I agree that the wheels look to flat right now and you I think that you are making the right choice by modeling out the indentations and hub. It will give to more depth and characture
Looks pretty good in the end - some parts that stand out as a bit weird are the wheels (very bright, and much more obviously photo-sourced than the rest of the truck) and the windows (quite dark, too saturated, looks more like painted concrete than glass - a reflection map would help this a lot, as would desaturating the…