Installing an amp and front door speakers is fairly easy... providing you have speakers in the rear doors already?
Out of interest how much is your local audio shop charging?
Would be better to install a four channel amp in the rear of the car, mounted to the back of the rear seats.. from there just run flat speaker wires to the back of the headunit (would take you 15 min to unclip the side trimmings of the door sills and then pop the back into place)..
Once the speaker wires are routed to behind the Headunit its simply a matter of connecting them to the OEM speaker wires in your loom. For this it would be better to buy a seperate wiring loom rather than you splicing into your original loom... or simply adding bullet connectors if you want to use your original wiring loom.. Now all your door speakers are running off the amp..
Door speakers themselves is just a matter of drilling through the rivets, installing the adapters if you need them, and drilling the new speakers back in...
Took about 3 or 4 Hours tops...