Your trip sounds interesting and we may have the ideas here to help you with
How many km a day do you plan to travel ? Will you be near improved camping areas with electricity or sources of fuel each day ? Many electric bicycles are now claiming a 60+ Km range per charge. Their motor is in the front wheel hub and battery pack serves as a luggage rack on back over the rear wheel. The battery re-charger is built into the battery package.
I don't know if the electric bike would be a better choice for less weight, bulk,
and being simple or not. But if you stayed at a place where you could recharge your battery each day while you rest or walk around the area to see the country side it may be a practicle choice.
It would be interesting to see you keep a journal and take some photos along the way and if you or your girlfriend has artistic talent, to do some sketches etc of the countryside, places you stayed, and other places of interest.