My plans are to run on my 1997 Sidekick Sport with the stock aluminum rims a P245/75R16  tire (30.5 in tall, 9.6 wide) with a 2" body lift and a 2" spacer.    I want to keep these rims and not change them .

This is going to be a Daily Driver that sees weekend State Forests, places that require 'high clearance vehicle'  and Day trips to some of the moderate trails of offroad parks that are within a few hundred miles of my home in Virginia.    I plan on locking only the rear (ARB) and will see a 2.3 motor .   I have my '92 Samurai on 36s for the trailer when I want to get crazy.

I've been reading and trying to understand about proper clearance with tires,     

Are my calculations OK for this tire or will I have rub?? what am I missing.   If I have to go with more lift, how much more?

I need to replace the front struts so if I need more lift, I'll have to figure out a longer spring/strut combo but am hoping that 4" will be enough for what I want. I plan on a winch bumper so spring rates will also come into play.

If I have to go with a smaller tire for my 4"  can I get by with a 30" even tall tire?

I'm still searching for my answer.

I think you will be ok. The Sport version might have a little bit tighter tire clearance due to the plastic cladding getting in the way. I had a 97 Sidekick (not sport) and I ran 30x9.5 tires for a while with a 1.5" spring spacer lift and a 2" body lift, no trimming. Later I moved up to 31x10.5 tires and all I needed to do was trim the rear of the front fenders back.

Since you mentioned plans for a winch bumper, I would not recommend a spacer lift since it only adds height but doesn't change the spring rate. Instead you should put on a set of stiffer springs, at least in the front, to counteract the extra weight of the winch and bumper. If you look at Rocky Road Outfitters, they sell the Old Man Emu springs (available in standard and heavy duty) plus a small spacer for a total of 2.5" suspension lift. The Emu struts are also longer than factory, so if you need to replace your struts you may as well get those. And then you can still add a 2" body lift to that and call things good.