Some more thoughts... As before, these are general rather than campaign specific.
Check out all the ports in and around your campaign area. The theory behind this is that _most_ ships, aside from "wanderers" and those trapped in a single system, will visit a starport at least occasionally.
I say "around" your campaign area too, because vessels don't always stay nicely within the confines of a single subsector. You will always have edge effects to worry about.
Find out what ports are present, and explain them. The results of these explanations will help you decide what is around.
For example, ports may be of a number of different types. They may be associated with the "good guy" pocket empire(s), the "bad guys", pirates, vampire fleets, local governments (friendly or otherwise), or may simply be places where Free Traders drop in regularly, or even base themselves.
There is no automatic way to generate most of these - some will be obvious - but using the Paranoia/Xenophobia characteristic from Path of Tears should give you some hints. For example, a low tech world with a high paranoia rating and a starport may well be a vampire or pirate base, or may be associated with "the bad guys". In the latter case, you could assume that their paranoia is lower when dealing with their "own" people.
From all this, you could start to deduce traffic patterns. High quality starports would tend to attract traffic, but if it is a vampire port, most -to-all such traffic would be vampire ships. Free Traders would usually work some kind of route, which may be a "loop", or may be centred on a particular base world. Pirates would generally raid an area around their base(s), but might trade with other starfarers, and mostly only raid soft targets. Traders may trade with both the "good guys" and the "bad guys", since such disputes aren't necessarily really their problem.
Traders will often know the worlds on their routes quite well, and be valuable contacts for wouldbe pocket empires - including the bad guys. On the other hand, they might also tend to flock towards "safe" areas, so as your PE expands, your merchant fleet would also tend to expand, almost irrespective of your attempts at recovering technology and upgrading your starports.
They will also tend to flock together for mutual support and protection, as well as mutual trade. So ports may very well attract relatively significant numbers of ships, or may just be bases for one or two vessels.
Of course, a "port" owned by a paranoid government may simply be a naval base supporting the vessels that will try to smoke any other vessel that sticks its nose into their system. This may even be true if the government is one you could eventually make friendly contact with.
And, of course, a world might well trade with well established partners, but be extremely suspicious of everyone else. You might want to have someone to vouch for you before you make contact. And there is a plot seed...