Generate 20-30 systems and pick the ones you want to have terraformed. Set up the jump point network for the first few transits. You do not need to fill every jump point with a destination, just those leading to the worlds you have designed. I would then save a copy of the database and while still in SM mode check what tech levels each ruin is for. Better yet, if you can go into the database and set them to the same race/empire and tech. Otherwise check what tl each is at, and if you find one that doesn't work for what you want you could go back to the original save and change it. Keep doing this untill you are satisfied as to the ruins that are left around for your pc's to find.
Brian