Unfortunately, multiple black holes isn't really practical as our current black hole solar is of pretty awful quality. I tried to do what you described in my interview submission and it didn't work out as well as I thought. What you see in the OP is a starsphere (background) we have in the files.
That black hole was decent enough. I used to take the bustard down into the mouth and sit there for a few, then jump out before taking too mich damage. It was a lot of fun.
As to systems, it seems systems are only cut or merged to scratch an itch here. The system layout and routes we had for years was fine! But no one is going to complain if new systems to explore were being chained on at the edge somewhere every so often.