That’s excellent information, very thorough! That’s about 25kg of vertical lift power per wheel that’s engaged, so at 30°, 50kg per engaged wheel. There’s no suspension on the vehicle so 2 wheels is the only guarantee for full traction but using 2.25-2.75 as the “wheel factor” is safe since it will rock to a third wheel generally. So 115kg-137kg for a vehicle weight on your slope conditions.
(Do check my math)
I agree a hub wheel is going to be the best, a CV shaft isn’t suitable due to wanting full underbelly clearance as a work area.
What’s the top speed up slope you would be thinking? 2mph? 5?