Wow! Just read this through in one sitting! First of all, I want to bow in admiration of your persistence and strength, pushing through every obstacle as you two did!
I live in Peru and have alot of experience on riding Chinese bikes in South America (even 2-up), and the worst thing you can do is just buy a bike and head out on a long ride! I recommend:
Seat the engine in (about 100 kms on these models) with a good quality non-synthetic oil before you load it and head off. Then change oil to a FULL SYNTHETIC 20W50 (made for 4T motorcycles) and use only that! It is AMAZING how long the engine will last! Top off oil (if needed) every morning. Just in case, carry an extra (next oversize) piston kit and cam chain (you can have both for less than $40 !).
Take it all apart (yes, new!) and putting it back together with alot of locktite and the correct torque (like those steering neck bearings! I recommend even replacing them with conical needle bearings).
Take some foam strips and pad the battery (they are always bouncing around loose!). Take some Dielectric grease with you (you won't find it in South America) and put it in every electrical connection. This will keep water and corrosion out. Secure good strong connections on the battery posts and then cover them with Dielectric grease
Gutting the exhaust to give more power and allow you to ride almost all altitudes on the same jet is very important.
Great rear rack but it probably added quite a bit of weight by itself. A steel one actually would have been lighter, but... THE MOST IMPORTANT THING is to triangulate the rear of it down to the rear footpeg mounts so the frame and rear rack don't keep breaking.
The stock rims on some of these bikes are paper mache! Best to find some tough steel or decent aluminum ones and have them laced up with thicker spokes.
Change out the stock 15/45 ratio sprockets with 17/43 ratio. Otherwise you will be screaming the engine at 50 kph. When you are going to do the tough spots, just put the 15T back on the front and adjust the chain! O-Ring chain. They are tough and quite inexpensive compared to back home. Don't leave home without one. And as they have much thicker links they don't stretch much! Use good chain lube every morning. Again at noon if it has been a wet day or many stream crossings.
KNOW where and when your rainy season is!
As your clutch wears the cable will get tighter. Make sure you always have some play at the lever or you will burn the clutch up! Carry an extra set of clutch plates with you (they are only $4 for a full set!) and know how to change them.
I've ridden Chinese bikes 5,000 kms at a stretch, well loaded (and me at 105 KG) and never had a mechanical issue the whole way!