What if I did a USB mouse hack (maybe use OSCAR mouse board) for all TBs and Spinners I use?
Is there a problem with having so many mice hooked up to PC? How does OS handle so many mice? Do they all control cursor at same time?
Complicated answer -
You can use one mouse hack with separate trackballs and spinners, but you will need a DPDT switch like shown here,
http://www.oscarcontrols.com/DPDTswitch.shtml, and you won't be able to use them both at the same time.
You can use multiple OSCAR mouse hacks on swappable panels with no problems.
If you use multiple OSCAR hacks on the same panel, all the mice will control the cursor, which is fine for single player games, for dual player games, you can use MAME Analog + or NoNameMAME to select which mouse works which player, but (since the mouse all use the same driver), if you re-boot, the mice may swap positions - i.e. the trackball might be mouse 1 and the spinner mouse 2, reboot, the trackball is mouse 2 and the spinner is mouse 1.
MAME can handle eight mice at any given time.