How do you know whether you can dock at a mission settlement without actually trying to land there?
The bases with the + signs after them are simply locations for missions to scan things, blow things up or destroy skimmers at. The + signs refer to the size of the base, 1 for small, 2 for medium, 3 for large. The security level is separate from the size and listed separately. They never have docking facilities, and there's no way to communicate with the bases, other than to scan things, blow things up or destroy their skimmers.From what I understand - which amounts to very little so salt pinches required - yes, those bases with + or ++ when looking at the planet from your system map don't like strangers much. They're local bases for local people; they'll be no trouble there.