cool building and love seeing a build come together neighbor...im also in your area albiet a little lower in elevation pursueing a very similar project...
i went down to O-ville and inquired about permits...holy shit what a headache. just to install a regular garage shop required a whole bunch of things i had to figure out. there have been many many rumors and even news stories about code department cracking down on illegal buildings and illegal terracing/greenhouses so good luck! up at 6k im sure you will be a little safer..
anyways i went a different route and got a commercial metal building and im gonna build out the rooms inside, very similar to your route except doing a mix of 2x6, 2x4, and uni-strut for the walls. no need to deal with silly permits or worrying about someone dropping a dime for code violations. now for my outdoor grow and the newly planned terraces, lets hope they dont see those!
What are you planning on doing to keep moisture down? Maybe up there in the hills in your climate it is dryer than down here in the lowlands... I have to believe you have good AC or good dehumidifiers planned. I think initially you are going to be sucking alot of moisture from the ground until it sorta stabilizes with the new structure on top of it (?? no expert here, i'm dumb actually) but then it will taper off as you hit equillibrium. I know you have plastic down already but do your research and don't go too quickly. If you have already done it man, more on ya.... I tend to make shit up as I go along, hopefully staying just ahead of my building progress....
My situation is very different and I can't describe my locale, but I'm pretty well sheltered already from the elements and I'm going to extremes to insulate and soundproof. However I still worry about moisture coming up from the ground so I installed Firestone rubber as a moisture barrier. This is very very thick and durable stuff. However 24x30 ish square foot would be very very expensive to cover with it. I'm using left over rubber from my koi pond so it was already paid for (notice I didn't say "free"... hehehe what is free?)
Peace bro, keep up the good work.