MO, Your outside (P3/P4) should be appropriately angled for screen viewing and the angle of your CP, not straight on.
Bad information. Dont follow.
A for the rest... some things to consider...
If you plan to use the trackball for arcade use... you will need about a 8 to 12 inch diameter of free space. As it stands, your hand would crash into the nearest joystick pretty easily, with a good spin. Buttons are not a problem, because they are low enough, and the hand usually arcs up as it follows through.
4 players - Make a cardboard mock up and have a few people stand at the controls. Make sure theres enough arm / elbow space.. as usually, peoples forearms flare out to a minimum of their body width.. but usually a slight more.
Visibility of the monitor for 4 players is not dependent on player angle. Its how far the monitor is from the player. So make sure to mount the monitor far enough away to give optimal viewing for everyone. Some cabs tilt the monitor back at a higher degree than others, to attain the needed distance.
(those cabs usually do not have 'blinder' side-walls... as that would block the point of sight on side players)
Angling sticks causes problems... because unlike a handheld controller.. you cant feel which way is Up on a mounted joystick. And... even from a side stance... your brain often thinks UP is vertical relative to the monitors position, rather than their position. Out of all arcade 4 player set ups, there are very few that angled their sticks. Most all of them are parallel to the monitor. Its merely the buttons that are angled, due to angled stance and thus altered hand position.