Hi David, thank you for your reply. After reading it, I called go! again, and they confirmed that they will *not* check bags through on United Airlines, so we do need to collect them and then re-check them. However, the good news is that there is a ramp to the plane, not stairs. So that's a relief.
If I had done my homework before booking, I would have chosen the Hawaiian Air flight which does seem to be much easier all the way around. But our tickets with go! are non-refundable, and the flights on Hawaiian Air are over $100 each.
I called HNL Airport Customer Service, who informed us that the wheelchair-pushers will take us to the wiki-wiki and that "someone" would help us getting our luggage on and off. So that's our Plan A, and we're anticipating that all will go smoothly. Nobody mentioned that there's a van, but we will ask about that when we get there.
Just in case, Plan B is to take a taxi from one terminal to another - it will be cheaper than losing our non-refundable tickets and rebooking.
I hope this thread will help someone else from making the same silly mistake I made. I was in a rush when booking and didn't do enough research. Our "cheap" tickets on go! really aren't, because of the $17/bag fee, and the hassle factor of not being able to check our luggage through.
On the bright side...hey, it's HAWAII
As I always say, "Even a bad day in Hawaii is better than a good day in NJ"