To add new rims you need to add them as addons like your cars, and load the folder where they are i assume.
There's an other way, but i'm not sure if it will work for all cars in the server but you can try to add them in the carcols.meta file in the section <wheels>
it looks like this :
<modShopLabel>Gram Lights 57d blue</modShopLabel>
WheelName is the name of the new wheel (file name)
WheelVariation is probably for when you want to have a different look when you make the tires using their "racing" variation (don't remember the name exactly, it's when it adds a white thing on the side lol)
modShopLabel is the name you can give to your wheel (only visible with trainers that allows them)
rimRadius is an obscure value, i always use this one
rear value idk what it is, i let it like that
You can add as many wheels that you want in a single car (or a lot before coming to the game limit), and you have to add a new <Item> content each time (copy pasting what's inside <Item> and below </Item> included, and make your changes for each wheels).
For the tinted windows, the thing i like to do is just making a fake glass shader by using the vehicle_badges from zmodeler 3 and playing with the texture transparency to get the visual darkness i want to the windows parts, and make them as tuning parts. This way, you don't just have the in-game 4 choices and you can even have colored windows/paintable windows.
But for that part, you need to know how to make a tuning part, and to apply in the end of the name the [PAINT:X] that you want (paint 1 is primary, 2 secondary, 3 is primary with livery support, etc etc all that is detailed in the zmod forum somewhere).
There's maybe a method to just add different tint options in the car files, but i never searched for that tbh, i like to control directly on the model what i do
Tell me if i'm completely wrong and you just wanted to really model in a 3d program those parts like your title says xd