Frankie:
First off, I might suggest you build the entire bar core from treated lumber & plywood. I lived in Naples Florida and the humidity can be nasty to OSB and untreated plywood.
Question 1:
If there is a level roof beam overhead, you can use that as the reference for cutting your leg lengths, otherwise shimming will work if you use enough of them to spread the weight. You don’t want a tippy bar. In my basement, I used the ceiling as a reference, measuring down to the bar height, then the remainder to the floor is the leg length…number each leg as you go so you don’t mix them up. I have a badly sloping floor too. Most basements have this problem due to floor drains.
Question 2:
You can omit either A or C or re-size A or C using the CHBD. B is not re-sizable using the CHBD, but you CAN re-size it manually. Remember, nothing is written in stone, some of the best projects use the plans as a guide, but there is no reason you have to follow them exactly.
Question 3:
A 34″ high fridge should fit – I am assuming you are placing it where the keg box is, right? Many have done it this way. The actual opening will easily fit a 35″h x 26.5″d x 20″w fridge or kegerator unit with a smidge to spare.
I hope that helps you.
Thanks & Have Fun!
Steve