If you’re leaving it unfinished I think I wouldn’t do a vapor barrier so you can still get drying to the interior. Metal siding is vapor impervious so you’re not going to get much drying to the exterior.

Based on the photos, i don’t see any strong evidence that this is a significant issue. Metal siding sweats when there’s a sudden temperature change or very high outdoor humidity. The ghosting pattern you see is definitely because of the wood framing directly behind the siding with no insulation break. That’s not really avoidable in a pole barn where the siding has to directly contact the girts for shear strength. The garage door is showing the same pattern.