If you do decide to use the holes in the doors, please know that the grilles will need to be shallow or you might bang your knuckles when winding the window.
x2. I had some there in my 75 and had to be really careful about rolling the window down.
I've had a few different speaker configurations in my dusters over the years.
First setup was 2 6x9's in the rear deck with 2 12's in the trunk -- huge amount of bass that seemed to wash out the highs.
I added some shallow 3.5" speakers to the doors and that helped with the mid range, but highs were still a bit overwhelmed.
Best sounding setup was 2 3" speakers in the dash, 2 5.25" speakers in the kick panels, 2 6x9's in the rear deck, and 2 10" in the trunk.
The 4 front speakers wired to front output of the stereo.
I know that seems like a lot of speakers, BUT you can get superb sound without it being ungodly loud.
One other thing. Spend some $$ on a good receiver, it will allow you to "tune" the system for the way you like to listen to music. A good deck will let you get the best sound possible even out of crappy speakers.
I prefer pioneer units. Something just down from the "premier" line. I don't really care about an animated screen, just something that has tons of audio adjustments and enough power to drive everything but the sub(s)
I'm currently working on ( among other things ) my setup and went with pioneer 5.25", kenwood 6x9's ( free ), and punch p1 12's because I found an almost brand new set at a pawn shop for dirt cheap...wish I had looked for 10's as the quarter panel boxes are turning out to be a real pain to build with how deep the speakers are.
You can see a trend here. $$ on the deck, cheap decent speakers. Most newer cars have decent enough speakers to meet the need if you've got a local yard, but there are lots of aftermarket speakers that are inexpensive.
The pioneer DEX-6600BT is the newer model of what I'm running. At $130 with bluetooth, smartphone control, high pass filter, sub frequency control and all kinds of goodies, it's a good buy IMHO ( I think I found my next receiver
)