If you want to work on stuff, 2 post 100%.
12 ft ceiling height is safe but not a rule. Would be needed if you're working on trucks.
I had a bend pak lift built to 11ft 5in for my previous garage. Have never had a height issue but I only work on cars and small trucks.
Also, whatever lift you get make sure you can get low profile arms.
Nothing sucks more than pulling your car on the lift only to have to jack it up anyway to get the arms underneath.
Not sure why you need to re-pour the pad but if it's in good shape 4" is good enough for any lift and the surface can be repaired if degraded.
