More speakers adds volume, not bass.
You can run as many 6.5's as you can fit in a door from one speaker output as long as you get the impedance matched. Also, be careful with bass in the front door as it might sound like a cheesed-off rattlesnake. I've been fitting car audio for 30 plus years now and never needed more than one woofer up front!
Dynamat is your friend...... buy plenty!