I'm guessing that 220w is MAX power (ie, irrelevant). What's RMS?

Patching into the HU location of the wires is definetly the easiest, it can be a PITA to get new wire through your door jam. I've yet to see a noticeable difference in larger guage speaker wire...so I would be confident in saying you're stock wire from the door to the HU would work fine, you've probably got something like 18gauge.