I have just come back from 2 weeks in Baja. As somebody has mentioned PEMEX did add another fuel stop right after Guerrero Negro. In fact from what I remember there's one before and after. The one before (when you are going south) does not have internet so you can only pay with cash. Make sure to have enough pesos. It's pretty close to the border of Baja Sur so if you can stretch it, then you can save the cash and pay with a card in Guerrero Negro.
Keep in mind that fuel now is something like $4 a gallon down there.
Download an app called iOverlander. It will help you in locating gas stations, free camping (though all beaches are federal land so camping should be free) and military check points.
I honestly would just stay with something like Michelin Pilot Road 4 or Angle GT tires for the following reasons:
On a hard packed dirt regular tires are going to be okay. You will have to slow down your speed anyway. Even with full on knobby tires you will get stuck riding on the beaches.
80/20 or 90/10 tires are only going to be marginally better off road compared to full on touring tires. Steering geometry and suspension of an ADV or a dual sport/ dirt bike would be able to take advantage of the marginally better traction. On the Streeple I don't think it would make a difference.
Roads were in great condition in April when I was down there. The 22mile section of route 5 is being paved and I would highly recommend against taking it.
I would look into the contacting Twisted Throttle and seeing if SW-Motech is going to make a rear luggage rack for the 765. Something like this:
They also have a fabrication shop at the HQ. They can always mod it to work on 765 as well.
Then just get a Rotopax mount
and you should be able to mount an extra 1 gallon of fuel. Maybe 2?...just depends on how much weight the rear luggage rack can carry.