My golf ball is not centered in the cup.
How critical is this to getting maximum performance? Seems like this would impact the cartridge angle.
It sounds really fine as it is, is there more to be had?
GE, your instincts are correct re: centering ball. IME you center it when the arm is over the LP side. You may have to also move the pulley a bit to get the pivot point central to cup, depending. At least I had to with my used Simplex.
Ditto previous posts on alignment and azimuth, except to add that you set azimuth with cantilever, not cart body, and as SteevA suggests, sometimes the play in headshell comes in handy with certain carts that don't like the 19 degree alignment as much.
This, along with getting damping right, are the most important ways to set up the table to sound it's best. Next, I'd say a good isolated platform and an aftermarket mat.
The frustrating part might be the trial and error process that may be short or long, depending on your cart and patience. However, diligence does pay off and the table doesn't go out of whack once set up.