I ended up getting a different freezer, but for the temperature control I picked up a single stage digital Ranco. Super easy to setup, and for a few bucks more you can get them prewired with plugs. You shouldn't need to make a collar to fit four kegs in it, so the controller should be all you need.
Usually you put the collar on for the taps, otherwise you might damage the freezer walls. At least that's what I have heard. I don't know what is in the side walls of the freezer itself. All you need is some 2X6's for a collar. I made mine with 45 degree angle cuts but I wouldn't do it that way again. Just butt them together and fasten them with screws. I attached my collar to the keezer with insulation putty. You can always use some party taps until you get around to making a collar.