I posted an illustration of my modeling process a pretty long time ago :
Illustration of my modeling process with Aston Martin DB9 - Pixels or Atoms ?. I've changed my move a bit since : I now work on only one piece at a time, trying to fully complete it before moving to the next one. And trying to focus on only one area at a time.
There is no particular order. I usually start from the hood, then front fender, front bumper, doors, A-pillar, roof, rear-pillar, rear fender, trunk and rear bumper. But YMMV : e.g. for my current Lambo, I started with the engine-hood, then rear end, sides and front end, just because I thought the engine hood was the most interesting part
Of course there is others ways of modeling a car. You mentionned one using a box, it's usually called box-modeling. I just don't do it, because I don't feel comfortable doing this way. So you have to try different moves until you find one seeming easy for you.
About stack of modifiers, I usually use only 2 modifiers : subsurf and mirror.
By the way : welcome to SMC, feel free to post your work as a WIP even you're not happy with it. SMC is used to provide good feedback, from complete newbies to accomplished artists.