there's a lot of opinions floating around on the necessity of expensive cables in car audio applications. IMO, you buy decent cable that fits your needs.
the car audio environment is terrible to begin with so any differences due to cheaper cabling is going to be inaudible.
as for speaker wire, just buy something that fits your power tranmission needs. 12AWG will work fine up to about 750W, 16AWG maybe up to 200W. you just don't want too small of a cable, because smaller means less ampacity, which means higher internal resistance, which means you have power loss on the cable itself, which means not all of your amplifier power is reaching your speaker.
12AWG may be hard to fish through the door grommets. so for you i would suggest 16AWG. find something with a smaller jacket so it'll be easier to work with.