I just finished my bar on Friday. I purchased an Avanti kegerator. My advice would be to buy the kegerator first. Get the Co2 tank filled, get a full keg and pour yourself a tall one.
Take the measurements of the kegerator and adjust the dimension accordingly. I thought I was going to have my hands full with the construction of the bar. It turns out that as soon as I saw the method for building the base, and then the method for attaching the countertop and the bar top, I hardly looked at the actual plans.
I put my kegerator on the floor as a freestanding unit. The bar has a back panel that covers the back of the kegerator, but the kegerator stands alone on the floor independant of the bar itself.