Update.
Cave is up and running. This was a root cellar in really lousy shape - black mold and rotted wood everywhere. After a thorough cleaning, a slapdash job with R10 rigid board insulation, foam, and exterior enamel, 2 coats; floor in deck and patio sealing paint, again 2 coats; caulked all seams, and ceiling insulated with faced fiberglass batting, and 1" rigid board. Back poured concrete wall, only a double coat of white wash. I had an issue with moisture leakage, originally, but believe it's now well-sealed, top to bottom (function, not beauty - those foam globs, "eh.")
Temp controlled with the coolbot. Performs brilliantly. With a room at only 216 c.f., the AC of 14200 BTU is way over the top, but that was by design, really - with the opening and closing the door in such a small space without a kind of transition zone, this sizing means I get back to 51F within 60 seconds or so. And especially given the insulation, the compressor really doesn't run all that frequently.
Humidity is controlled via a 120 VAC PID controller, which I've simply wired to a plug in which I've two ultrasonic humidifiers (Crane "Teardrop"), which really pour the fog on, as needed. Now that I've got the controller, I've halved my RO water usage, which is the only real drag to using these humidifiers. But I didn't get very good results using my existing, 4 gallon Graco evaporative humidifer.
Anyway, cave runs at 51F, with RH between 92-94F (there are some zones, which oddly started today....I switched the cheeses to a new shelf as I do have some mild black mold spots on the top shelf, and the affected shelf was taken outside for a boiling water, salt scrub, sunshine bath. This upper zone now reads 85F, but I wonder if it will even out overnight. 92-94% everywhere else. I don't really mind, however, as it's nice to have a shelf with this lower RH, and it is also a kind of sacrificial shelf, in case I get some ceiling condensity (so far, after a few weeks, no condensation anywhere, knock on wood).
The last phase before I can really kick into my desired gear is the completion of a true alpine, screw-style cheese press. It will handle my Abondance form of 20", and I'll be doing 20 gallon vats soon. I hope to have it finished over the next couple of weeks, as I'd really like to capture the last of the summer milk. I use rennet paste currently, but am working with my French supplier to get dried veal vells. I use a twin temp incubation whey starter, thanks to Pav, Alp, and Jim Wallace of New England Cheesemaking Co. for helping quite a bit in informing my thoughts here. I also use a very small percentage of Alp-D. (This is for my Abondance-form cheese).