In terms of MP, pretty sure OKW's MP costs for total tech is less than everyone else and their healing (which everyone will get) comes with T1 explains it.
200 for each truck, 300 for retreat point = 900 MP.
Including cost for retreat point as part of normal tech makes as much sense as including reinforce trucks or forward assembly as tech. Only USF get a retreat point as part of teching.
You did forget that each truck cost 100mp to deploy though, so it ends up at 900mp anyway
. Which is way to cheap compared to the others(brits come close) and part of the problem. If you take into account the starting resources and value of starting units(what you get for free every game), and subtract it from cost for full tech, it ends up at ~250mp, compared to SU ~750, OST ~630, USF ~600 & UKF ~500 (not including bolster squads). The difference gets lower if any tiers or upgrades are skipped of course (i.e. t1 & molotovs), but that comes at the cost of diversity/utility. And OKW can arguably skip mech truck in the same way (very risky, map dependant and situational unless 2v2-4v4).
I think OKW is pretty much fine fuel wise so any side upgrades should have their cost focused on mp, not fuel. A similar cost to medics as the other factions, as you mention, would be a good start. Flak Truck should have a cost as well (munitions probably), it's a low risk, highly performing cutoff guard at the very least, if one don't want to put it aggressively.