Modeling a car, theory questions

I’d like to ask you a few questions about car modeling.
I’ve made three models in my life, hovewer, they are far from perfection.

  1. How should look the topology of a car? I saw that the best shading is on an object based on quads.
  2. How to split doors and openable parts like the hood and the boot and the rest of the car to make nice dark seams? Storing them in separate objects make the changes difficult and it’s hard for doors’ (and other parts’) shape match the shape of the car.
  3. Are there better and easier solutions than edge creasing to make some edges sharp, when using subsurf? Sometimes creasing causes problems with shading nearby faces, especially triangles (that’s why i say about quads in 1 point)

The car I’m modeling now looks like this at this moment.

Does it have too much vertices? I think yes, because its hard to make changes to it. But using more than 4-vertices faces gives strange shading. So I was using a lot of loop cuts to make topology consistent.

The last question. Which tools do you use most when modeling a car? I was using this time Knife, Loop cut, Edge crease, but I wonder if there are better tools than these.

Yes, try to keep it as a quad only mesh when using subdivision surface modifier. Quads subdivide predictably and are easier to work with.

Creasing won’t do a good job on its own. You want good topology and use perimeter loops to sharpen the subsurf result. In short, make a loop cut and slide it near another edge loop and you have a hard edge.

If you can, model the parts as one connected geometry and separate afterwards. That way you can cut them and the shape will continue when the objects are separated.
You can rip an edge by selecting an edge loop, put your mouse cursor in which direction you want it to rip, and then press V. If you separated so that you have two parts, you can select it quickly by selecting something on it and press ctrl+L to select the rest.

Thank you for your anwer. Ripping edges was what I needed for nice seams (instead of separating objects by P key).
It’s a pity that there arent nicer and cleaner ways to achieve sharp edges without additional cuts and creasing, which doesn’t always work as good as we wish.