4" of BS is the most common around here with the 16X7 that is.
about the spare from my experience its very useful to have a full size if u offroad a bit cuz the liberty will drive weird with different wheel heights well any car would but with a lift it sort of amplify the effect
plus the new wheel with a full size spare will look way cooler on the back than any other mod u can think of

(my opinion

)
as for the spare mount i have 245/70/16 full spare, no spacer and the window is very much clear with half an inch difference (one side) i would say that you shouldn’t need a spacer either
hope i helped