I believe it does take into account your current avg MPG, and if you drive somewhat hard like me, then definitely yes, If a little less than hard, then still, probably yes. lol. As for your other part, Big Blue or Mk will probably get on here soon to answer your question. lol.
Ha! too funny! I have lots of time on my hands right now while I am 'away' for work.
The MPG will also add in idle time also. I had that when I would warm up the rig one icy days, so it takes the total time the motor is running, moving or not, in the calculation. That has been my experience so far.
Big Blue has the really helpful link set for just about anything Commander that you could want, I really need to keep that handy also.
I am the one who is going to tell you that before you do anything with your new toy, get all the maintenance done that is not normally touched by the dealers/owners.
Transfercase fluid change, differentials fluid changed, Steering tie rod ends, buy the hard vacuum line kit from the dealer and change out the vacuum tubes on the top of the motor, PCV valve, remove the throttle body and clean it with TB cleaner.
Once you do all that you will have inspected most of the vehicle to get a sense for what you will be touching for the lift. The 2.5" lift kits available are are pretty standard across the brands and well supported by the vendors.
I am a real big fan of maintenance first because lifting will stress parts that may be good with stock stuff, but will fail under the increased stress from a lift. This way you may fix a problem before you do all the lift work and not have to go back under it a hundred million times looking for the squeaky bushing/bad ball joint.
Besides nothing says you care for your rig more than having new parts in the odd places nobody likes to remember... tie rod ends