I am currently building a fermentation cabinet from scratch, and using the guts of a mini-fridge for the cooling portion. I am using an STC-1000 controller, and will either be taping the temp probe to the side of a carboy, or purchasing/making a thermowell to put down inside of the most recent fermentation that I put in the chamber.
I am using a dual front door approach on mine. It will basically look like a kitchen cabinet, or piece of furniture, with two equal size front doors and a solid top. The coils of the mini-fridge will be attached to one side of the chamber, with the compressor sitting on a custom shelf at the bottom.
I used 3.5" of rigid foam insulation on the top and bottom, 2" on the back and sides, and I've got 2.5" on the back of each of the doors. I also added rubber door weatherstripping around edges of the insulation, so that when the doors are closed, the stripping is compressed and creates an airtight seal. All corners are caulked and tape with aluminum HVAC tape.
I am using either 1 or 2 heavy duty computer fans to circulate air past the cooling coil inside the chamber when the compressor is running. I don't foresee needing a heat source, but if I do I will probably use a ceramic heat bulb (like you would use for reptiles).
I don't think there's any reason you can't keep it front loading, rather than top loading. It just takes a little more diligence in insulating and sealing it. If you want it to be easier, then seal the front and make it top loading.
I haven't started a thread or posted photo's of my build yet, as I want to wait until its completely finished and running, but I could add a photo or two here if you would like to see how I did certain things. Just let me know.