Strip model with submeshes to prefabs or not?

Hi! I have a car models with some spoilers, some guns and such. I've created each model in a 3d editor and imported to unity as a single fbx for each car.

Now, I put each model on a scene, strip it to the chassis and create lots of different prefabs, like "spoiler1" or "gun1". Then I create main car prefab with chassis and wheels. The plan was to instantiate prefabs as children of main prefab, they are placed accurately where they belong.

I have different cars (they all have submeshes), they use same materials. The things is i get way too much draw calls.

The question is: Is it a right practice to use customization? Does every prefab made from one model loads it(model) to memory each time or not? Or should I create a single prefab from model and hide or show children?

Thanks!