#1: You need CDVDpeops to run a legal disc from a DVD drive.
#2: You do not need rom1,2,erom, so don't worry about it.
#3: All you need in the BIOS folder is the main rom0 (4MB is size, normally badly named to something like SCPH10000.BIN / SCPHxxxx.BIN).
#4: CDVDnull will only allow you to execute a PDdemo ELF or run the bios, hence called 'null' eg, no CD / CDVD.