Re: New Project - Help Please!
Sounds like a heck of a trip! Have you done any cyclotouring before or are you starting big? Putting a motor into this situation is going to require some planning. A gas motor setup would likely be problematic since you intend to pedal most of the way and most gas systems leave some kind of drag on the drivetrain when not running. There are a few ways to decouple the system, but I doubt you'd want to deal with all the extra overhead of a gas system if you're just looking for an occasional boost.
You may run into trouble on the electric side with flying with the battery banks. Airlines are all introducing new rules about batteries in baggage due to explosion risk, so something more to look into there, I'm not real sure what the rules are right now and they are changing. You may need to ship the batteries to yourself outside of normal passenger airline handling. You could make room for a battery on your current set up by adding a front lowrider rack made for touring, this will also help balance out your load in general. Adding a hub motor would be fairly trivial like Davezilla said.
Charging could be an issue as well if you are planning on camping, do you know you'll have access to power along your route? Are you staying in central america or heading south as well? If you're getting down to south america, there are different voltages, but everything in CA uses 110v with our same plugs.
In terms of a tour that long, you are likely to break something. You will certainly have flats. You can use 26" tubes in a 29er in a pinch but it's not ideal. 26ers are still more common just about anywhere than 29s. You'll want to be carrying a number of spares and a patch kit no matter what wheel size you use. For safety sake I would also carry actual spare tires and not just tubes. Unless you're planning on a majority of dirt roads, I'd be looking at slicker tires to decrease rolling resistance over the long haul. I'd also look at putting barends on your bars just so you can change up your hand positions occasionally. I'd also be looking at full fenders for your bike rather than just the "crud catcher" style you've got on now. They will keep not just you, but your components cleaner if the weather gets messy. Got lights on that bike?