[Gromit]

You are on the right track with American Autowire - my advice would be to get their plug and play kit to hook up using the OEM connectors all the basic stock GM essentials as designed by the GM Electrical Engineers; and then if you still must go look and pay for all these exotic backyard and unknown local service providers to hook up the few remaining outliers stuff that is not stock. it sounds like a good argument for keeping things stock but that is just me...