Node ownership will be kept on a spreadsheet updated by the managers; updating the nodes every week can be a real pain, so thats not going to happen.
If you don't want to have to keep making more nodes, could you make a decent size map(say 85 nodes), we'll just list certain ones offlimits until we get to a certain size. Say we start off with the central part of the map (17 nodes), label them with an A, to the top of it 17 more nodes(label B), below 17(Label C), right 17(Label D), left 17(Label E)
We'll start with only the center ones labeled A, when we get big enough we can start using the B sectors. Et cetera.
We can have nebular missions as well, those can be fun

So you can put maybe 2-3 nebula sectors per map section(likely to be jointed with each other).