Update time:
So I have the proper parts sourced, and should be able to handle the current quite well. The max running current will be 8A, and everything is sized to at LEAST 15A. The PCB traces have been sized so as not to increase in temperature by more than 10C, which is VERY conservative. Current spikes and the like are also being accounted for based upon testing on the on-car motors. I have PCB's designed up and ready to be built, though I think I will use the small empty spot on it to put in some extra "thermal protection" components.
For the sake of keeping the packaging simple, I will not be making the activation delay adjustable. I will do some "ergonomic" testing to get it feeling good.
This unit will control the driver and passenger windows. They will have one-touch up and down functions. There will also be an option to put them both up or down from the driver's buttons.
After this I will look into adding sunroof compatibility. Thereafter, I will see about a 4-door controller. Anyway, I hope to have a prototype going by next week. I am going backpacking for 5 days next week/weekend, then begin work at my new job. Rush rush rush!