So no FTL for at least the majority of you game, and only STL drives. And everything is within 80AU of each other (and probably less than that). So what kind of travel times are you looking for? I assume you aren't really interested in sub-1G acceleration in that would make for very long travel times even in a very dense setting like this. Weeks to cross the setting? Months? or maybe just days?
It sounds to me like you are aiming for a Serenity/Firefly type setting which would normally take a few weeks to cross the setting. I'll have to check my math again but I suspect a Fusion torch drive would work for you, as would a grav drive as described in SF Xtreme (but maybe with lower accel factors). The questions that you would need to answer are 1) Is there artificial gravity and inertial compensation and 2) Is there a limit on the top speed your ships can reach (limited by shields, limited by fuel, limited by time, limited by crew requirements, etc.)
So I am pretty sure I have material to cover a setting like this.
In case you are wondering what material I would use for this:I would probably recommend a fusion drive with low power grav generators (1G max) with no inertial compensation. So Accel factors around 10 Gs max (limited by the crew) and top speeds in the very low fractional light speed area (limited by the lower acceleration, and the stellar dust against the hull or particle shields). It would takes weeks or even months to cross the 80AU diameter disk but most destinations would only be days apart. At 1 G constant Accel and a flipover 1/2 way that means something in the vicinity of 3 weeks with a top speed of about 12%c. That is a bit faster than I would push things in a dust cloud so call it a month with a top speed limit somewhere around .05c. I would also recommend a particle shield even if the setting doesn't have other defensive shields. - Be careful with these numbers, I haven't really checked my math very well for this post.
Thanks for your feedback, I am trying to make sure I have ideas available for most of the games out there.
Regards,