As a construction manager I can tell you the only thing I've seen done for insulation that you can still reach is to insulate the edges of the slab down as far as you care to dig. I've always wondered at the value to this but the experts specify it in cold climates. Use as thick an insulating foam board as you can afford.
As to moisture, there are products on the market that are used to stop leaks in basement walls that may also work for your floor. Burke and Sonneborn are two of the major brands. Google the subject for more info. Don't forget any application usually requires a very thorough cleaning/prep of the floor. Unless it's relatively new this is hard work.
If your floor is of newer vintage we most always put a vapor barrier down and the sand is used to both protect it during the pour and allow moisture to get out during the early curing. But if you know it's not there, and it's often deleted under non-living spaces, then the sealers may be helpful. I'd also consider using a sealer that would be compatible with a later application of epoxy floor paint should you wish to go the final step to a really great shop or hangar floor. The epoxy alone solved my garage problem but in a warmer climate.
Good luck.
Dave V.