1) yes it will work providing the leak caused no other damage to the pcb. The unibios will not remember its region settings however.
2) I am not sure given hiscore saving has not been fully tested with MVS.
3) No idea about that one.
Whats different about the Pacific bios?
Correct yes, which is where i got mine. Cause the LAI NEO-GEO cabs here had buttons to allocate credits to one stick or the other.It is also known to have only been installed in early 4 slots.