Once they harden off a bit make sure to cut the taproot when you transplant into an inorganic medium. Try to minimize pruning at least for the first few years, this species can grow really fast and thicken up pretty nicely if you don’t mess with it. I made that mistake with my seedlings about 5 years ago and I feel like they are just now recovering. I think it’s because this species tends to retain its needles for a long time, so its pretty traumatic when they are removed. In nature they can retain a set of leaves for up to 20 years!
The other downside to the long leaf retention is that they can look a little funny; sometimes they’re called foxtail pines because the needles hang around so far back down the branch. But I think once a branch is long enough it’s OK to thin old needles. The upshot is that they backbud like crazy, and the needles are naturally quite short. I think this species requires a lot of patience, but has the potential to be a really beautiful specimen, similar to Japanese white pine but with a distinctly alpine feel. Good luck!