[Build Help] I don't know where to start on my shopping list for the system I want to install.

So I plan on installing an aftermarket deck, speakers, and subs in my 04 Buick LaSabre for my birthday which will be coming up in a couple months.

I have never really done this before. I can figure out the wiring but I have no idea where to start when looking for the hardware as far as compatibility and sound quality. I know my car would need 5 1/4" door speakers and 6 x 9s for the rear. I also want to install a subwoofer but know even less about those than I do about the speakers. Any help or links to anything would be greatly appreciated. My budget is somewhere in the ballpark of 400-500.

Thanks again in advance for any help you can offer.