Emulation Station will currently see these files:
.bin .cbn .cue .img .m3u .mdf .pbp .toc .z .znx
Some info on the Wiki here:
https://github.com/retropie/RetroPie-Setup/wiki/Playstation-1
Good tip there about the BIOS (although libretro-pcsx-rearmed does have a basic inbuilt bios that will support some games)
I’ll try to do a video on PSX soon – but its pretty easy unless there are multiple tracks/CDs. (I take .cue out of Emulation Station so it doesnt show duplicates.)