Hello SnifflingDarK and welcome to Ngemu forums.
ePSXe doesn't use pad plugins, you'll need to stick with the internal built one.If you want to use pad plugins, emulators like SSSPSX, PSXeven or PCSX will allow you to do it.
Also,for mouse control, there is an option in the controller plugin of ePSXe called "Digital/Mouse", but as I never tried it, I prefer let someone more aknowlegeable than me to talk you about.