The Max No of systems only limits the maximum range of the system IDs, it does not cause all of the systems to be generated. so the effect of it really only affects clustering (ie how soon you will get linkages between systems, not counting the Local system effect).
The number of systems in the database is controlled by how aggressively you (and any NPRs) are exploring jump points - I've rarely seen more than 1000 systems in any of my games unless they have been going for 50+ years, or have 5+ NPRs.
Crash errors tend to be more of a function of the number of NPRs in the game than anything else (largely because AI is soooo difficult to program, you can never get it good enough to cover all possibilities), but there's no hard and fast rule there. I dont often have campaigns end due to crashes these days - its much more likely to be due to RL (tm) issues or simply losing interest in a particular storyline.
