A five gallon cornie is 8 1/2 inches in diameter. The practical (including valves and hoses) height is 26 inches. I'd estimate you could put at least 16 kegs in your freezer. If it's like my smaller freezer, there is a hump in the bottom at one end where the compressor is located.
I'd recommend keeping your gauges inside the freezer to minimize holes in the case. The regularors rarely need adjustment. My freezer actually has the condensing coils built into the front and sides, so cutting holes anyhwere other than the top would be tricky. Plan on having a dual regulator setup, so you can have more than one delivery pressure. For my "real ales" I use a few psi, just enough to deliver them. IPA's etc. need a little carbonation.
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