Colby,
I've done san francisco to San Diego on an MB while towing a 9'6" longboard to boot. A very fun trip. For the boards, we used burley cargo trailers and just strapped the boards upright on the left side. I've also done a ton of MB touring. My whole frame and drivetrain are somewhat custom, but I do use the subaru EH035 engine and the staton gearbox. I have not had any trouble with those components. I have, however, blown up quit a few freewheels on the gearbox. Because of this, I'd recommend upgrading to the White Industries freewheel (staton sells it). I have several thousand miles on mine without a problem, so it's worth the extra dough IMHO.
I'd also recommend against a cruiser. The geometry is comfortable for a trip to the bar, but gets very uncomfortable after a long day in the saddle. They put too much pressure on your butt. Something like the Surly Long Haul Trucker would be an excellent base for what you have in mind. It'll be comfortable for all-day riding, it's steel, so it will hold up to the load. A rack-mount staton kit and an LHT frame would be a nice setup.
I have no experience with the staton shift kit, but running the engine power through the gearing would be very helpful for your proposed route, especially up near Big Sur. But if not, you'll want to gear pretty low. I've toured with a friend who has a staton friction kit on a specialized 29r, and he always uses the smallest roller available (lowest gearing) due to hills and trailer towing. Maxes out at about 29mph, but still pulls (with a lot of pedaling) most hills.
My general advice is this, treat your tour like a regular bicycle tour, expect to pedal most of the time. if you do this, you'll get a lot of exercise and your butt will hurt less, and you'll realize how rad MB touring is because you end up averaging 20mph, rather than 12.
Anyway, let me know if you have any questions. I'll tell what i can.