Very interesting stuff, Im gonna pop off and look at your dallas temp probe wrapper in a sec.. im embarking on a brew controller at the moment but adding a few more 1 wire ds18b20 probes to stretch over to the FV's wouldnt be a problem, tho im controlling them with stc100's with the + firmware update to include profiles.
being way behind you on my road i cant offer much help on the arduino side, nit that u seem to need it just encouragement..
However i can urge you to seal up the seams of your box, as the cold air inside will flood out given the slightest opportunity, a fellow with a similar box tracked down the root of his fridge compressor running overtime down to a paper thin gap between insulating boards.. Cheers