Start with 5 "possible" Wear. Mark 1 of those (remove it) when Wear is taken to your glider. Add "possible" Wear back through repairing your glider. Reach 0 "possible" Wear and you cannot use mods. You got it right!
Guild of Sand is only found in Desert locations. When you find them then you can perform Settlement Actions there, as well as interacting with them. You cannot find Guild of Sand representatives in Settlements outside of this action. The Caravan Friend reward is only for level 4 members, which aligns with the requirement for other Guild special rewards (I missed adding the Bond Level 4 requirement, sorry!).