I have a 7.0 cu. ft. GE that holds 4 ball lock cornys on the floor as well as my 5 lbs. CO2 tank, also on the floor. I went with a collarless, coffin style keezer for my build, so 4 is my maximum, unless I used a 3 1/2 gallon keg on the hump. I'm reserving the space on the hump to put an Ale Pale for lagering, if I want to attempt it. If you were to put a 6" collar on the thing, you could fit another keg or two on the hump. I'm not sure if you are going to be able to find a smaller profile chest freezer (7 to 8.4 cu.ft.) that will hold the kegs in 2 rows without staggering them. You may have to go up to a 14 cu.ft. for that.
Are you going with a collar style keezer with the taps mounted through the collar or are you building a coffin style keezer like mine, with the taps mounted on a coffin on top?