I recently got a Wilson Combat BUIS from the EE here. I must say, it is a VERY rock solid BUIS, and I am very pleased with it thus far.
The clicks are very distinct and crisp and the mount folds up and down easily while holding firm.
I'm going to take it to an indoor range to set it up for a 50yd zero. Later on I'll actually take it out doors and strech it out some more.

I have a YHM gas block mounted flip up front sight. Should I be using the rear BUIS elevation or the front post for elevation adjustment?
Would it be best to just position the front in a neutral position and take care of all the elevation adjustment with the rear elevation?

Should I ditch the gas block mounted flip up sight and opt for a rail mounted front sight?
This way, I won't have to re-zero if I need to adjust my gas block for any reason.

Zero out your Wilson BUIS elevation and windage knobs.  Zero your rifle and use the front sight to correct for elevation.  Once you are on target for the elevation, use the elevation and windage knob on the BUIS.  

How do I know when the Wilson Buis is zeroed out?
Just see where it bottoms out and count the clicks until max height... then go to the middle?