Midrange decision is probably the most crucial. Placement is everything, so whee the speakers can go determines size. I would take a set of full range point source drivers in the dash over anything else. But not all of us have a vehicle that can pull that off. Separate mids and tweets are used to give airspace to the mid and mid bass while the tweeter sets the soundstage height.
You want mids as far from you as possible, aimed at you. Kicks work well, but kicks lack airspace for mid bass. You can vent the kicks, then your struggle is structure borne vibration and resonance. Solve those, and you are sitting pretty good at building a two seat car. We use the doors because it is easy to get mid bass once we deaden and seal the doors up.
I've heard great 2-way systems. I've heard great 3-way systems. Install is everything, and I focus most time and effort into speakers up front, working to get a proper sound stage with driver placement and T/A.
Subs are last, because until you determine what you can do for mid bass and overall music volume, you don't know how much bass is needed. Subs should fill in but not take away from overall balance and instrument location in the sound stage. When you hear bass that seems to come from the dash, it's pretty cool.
Good bass is difficult to achieve, especially with standard methods. A box in the trunk hasnt impressed me since I started to appreciate accurate reproduction of music. Custom integrated enclosures usually work best, taking phase interference into account.