Need help with optimization and exporting

Hello everyone,
I’m new here, a game developer just picking up Blender. I’m coming from a C4D background. Anyway, with two days of knowledge in Blender I managed to create a wheel/tire for one of the main vehicles in this game I am working on (picture attached).
It’s not 110% perfect but I’m quiet satisfied with the end result, mostly without using tutorials (except for the tire treads). The problem now, though, is using the wheel for practical application. I wanted to create a new (blend) file and I thought maybe I could export this wheel and import it into a new project and simply re-size it. But that’s not the case…

First of all, when I export it (doing so as an .obj file), it doesn’t seem to retain my texture styles/objects.Like, the rims are actually a very dark blue gradient with a reflective (mirror) surface. But when I export this model, it doesn’t retain the color and that mirror service. Why is this? Secondly, my wheel is a massive file (I like to build big and scale down in the end). When I scale down the model, though, it doesn’t seem to be helping with the sides. My wheel (the tire specifically) has too many matrices. I got this program “meshlab” to help with that, but still, I can’t get the model to export.
Does anyone have any exporting advice? I basically want to scale down the entire thing and make five copies of it (six wheels total). Thanks for any help in advance, I would like to become a contributing member around here once i learn the program a little better!