Hey bigpapa7272....what style of keezer are you going for....collar? coffin?
I recommend at least the 7 cu.ft. freezer with 4 kegs & 4 taps. I also recommend a dual body regulator with a 3-way manifold off of one body, with the other reserved for carbing up a new keg or for styles that require a little higher carbonation level. Most 7 cu.ft. freezers will hold 4 cornys on the floor as well as a 5lb CO2 tank....not sure about the 7lb tank. If it's the same diameter as the 5lb, but just taller....it wouldn't be a problem, but if it's much larger in diameter, it may be tight.
In retro-spect, I love the way my rustic keezer turned out and I get compliments from everyone on it, but I only installed 3 taps, eventhough my 7 cu. ft. GE holds 4 kegs. I figured that I could always have a "keg in waiting", but once a keg carbs up....I want to start pulling pints, so I'm moving around beer lines all of the time. I'm adding a 4th tap, but it's a P.I.T.A., because I knifed a log into a custom trim piece where the taps mount and now I have to start the process over and knife a new trim piece to accomodate 4 taps.
Good luck with your build and keep the thread updated, so we can follow your progress. Cheers.