You'll have to create 48 ringworlds and make about 150 planets out of asteroids to get near the 500 figure. I'm pretty sure that's about as many as you can reasonable expect to get in a game. Even if you do generate a 39 system quadrant, chances are pretty high you'll wind up with at least one black hole or nebulae. Without a good map, I don't think it'd even be possible for someone to reach the score of 278.7M that I finished with on this one.
As for actually getting those ringworlds built, I found that I got a much quicker start by demanding the AI give up and surrender to my fearsome empire.
Just as using troops to take over the AI HWs is more effective than just glassing them all, threats and diplomacy (after putting a chokehold on their economy) works better than troops. If I'd had to use troops, I might not have gotten a score half as high.
-Drake