Your questions are more Eclipse related questions than openHAB. You may have more success on Eclipse forum.
But now I wonder whether I should tick “Add project(s) to working set”, or not…
A “working set” is just a convenience to organize your project in group. You can open/close them all at once, or find them easily. There is no impact on code or anything else.
(And what with “Resolve Workspace projects”?
“Resolve workspace projects” means that Eclipse can, when running / building, use directly the project in your workspace to find dependancies, instead on relying on your maven installation .m2 directory.
The idea is (I think) avoiding building/installing with maven every time you make a change in a dependancy project.
Is that okay? Or should something be fixed? I can “run” the openHAB demo version without issues.
I don’t really know for this one, but I think that if it works, then don’t worry.