John Wayne Airport is near the intersection of the 405 and 55 freeways.  There are many good chain hotels (Hilton, Crown Plaza, etc.) in the area and its easy to get to from any direction.  There is no freeway that goes all the way to the Newport Beach harbor, so you may be placing yourself  further from potential customers if you stay near the ocean in Newport.  I think I ma typical in that part of my decision on who to see will be calculating the drive to get there.  Costa Mesa is centrally located.  Anaheim is a good choice if you are wanting to also attract customers from LA.  Many hobbyists will make the drive to Anaheim, but not all the way to Costa Mesa.

and make sure you screen like crazy. Some parts of OC are incredibly hot. Definitely stay away from "motel row" type places - and some of the higher end hotels particularly by JWA require keycards for the elevators, so that's a good thing to find out ahead of time.
I'm reluctant to post hotel recommendations on the open boards but you're more than welcome to send me a PM and I'll be happy to pass along what I found out on my research for my own trip to OC next week.