Congrats on your new Class C. We were in the same situation 12 years ago and this is what I would do differently now. First, there is no problem free new RV--there WILL be issues that need to be resolved. So for your initial trip(s) I would not take an ambitious journey. I would take a shorter trip(s) near you to get acquainted with your C and to be able to get back to your dealer should problems arise. Also, I would take the RV out in the RAIN to check for leaks. Don't wait until you're ready to take a long trip only to find that your roof leaks. Since your RV will be ready in Sept, take a short trip up the coast in October where you should encounter rain showers.
As to where you should go on your first long trips: ANYWHERE! Just go--there aren't really any bad places to go...and if there are, just get back in your RV and go someplace else. Everyone tells you about their favorite places and why you should go there. I would listen to RVers who tell you where to avoid (mosquitos, weather, costs, crowds, etc). Happy Travels.