I assume you plan on tying the trackball/spinner into the player1 controls?

Not really. MAME supports them as analog devices entirely separate from the joysticks... But I was gonna throw on an extra button or two near the spinner/trackball wired into the same input as player 1's buttons.

We had slightly angled ours to let ppl stand slightly off to the side, does NOT work well at all, had to go in and remount the joysticks.

Thanks for the tip. Players 1 and 2 (with the seven buttons) will definitely be perpendicular. Players 3 and 4 are kinda off to the side and I'll be careful with how I position those.

Other than that, the 4 player ipac should work nicely.

Ipac, schmipac. I'm using 4 Microsoft Sidewinder joysticks. No need for an Ipac.

Oh, and the trackballs are VERY expensive. ~$100 US for just the trackball alone

My Imperial trackball (already purchased) was $80. The spinner was another $40. Not bad if you ask me.