One thing you should add are 10K resistors on the pic IO's to the motor chip. Check the spec sheet to make shure your version includes internal clamping diodes. The TI sn754410 does. If you are going to run the motors at close to full load get a clip on heat sink for the motor chip. You could add a diode for reverse battery protection. The pic chip mention I don't believe has the capability of generating 2 PWM signals to control the motor speed . You would have to choose a pic with an ECCP. The other way to go is buy a motor control board that has a pic on it and comunicats with the pic chip by serial ttl commands. Some boards have current draw feed back and status monitoring. Check this link.
http://www.pololu.com/products/elec.html#motocon