Hi Brent - congratulations on your Gateway order! Exciting!
I'm guessing your dealer is Lakeshore RV as you're making a trip to MI to get the unit. As it's unlikely you'll utilize your MI dealer for warranty service, if your schedule allows, consider staying in the area for a couple of days to really put the coach through it's paces, all the while, keep a list of issues and questions. Then schedule with your dealer, a return to their service department for punch list items and answers to your questions.
Doing your own PDI after the dealer does theirs is always a good idea. Some dealers are more sensitive than others about allowing the customer to do their own PDI or giving the customer the amount of time they've requested. I suggest you speak to your dealer salesperson about this soon, so you can both get on the same page in terms of expectations on both sides.
I see Jim (Oregon_Camper) has linked his PDI form in this thread. I hear it's pretty comprehensive.
Hope to see you at a Heartland rally next spring!