well, ok if you insist 
as far as i know, most adapters are based on the same design. In the case of USB, it's the one by Simon Nield:
http://www.stndev.btinternet.co.uk/usbpads.htm
so you can estimate your answers from reading that.
i dont think it has 4 player adapter support. You don't need it anyway. I think you can connect as many of those usb adapters to your computer as you want and have usb ports for. no one i know have tried it tho.
and unfortunately, no PSX emu has added support for more than 2 controllers yet. (some arcade emulators support 4 players, i think)
as far as i know, most adapters are based on the same design. In the case of USB, it's the one by Simon Nield:
http://www.stndev.btinternet.co.uk/usbpads.htm
so you can estimate your answers from reading that.
i dont think it has 4 player adapter support. You don't need it anyway. I think you can connect as many of those usb adapters to your computer as you want and have usb ports for. no one i know have tried it tho.
and unfortunately, no PSX emu has added support for more than 2 controllers yet. (some arcade emulators support 4 players, i think)