the purpose of a roller nut is to prevent the strings from sticking like happens on a regular nut.when you turn the tuning keys your strings stick a little in the grooves which makes tuning a little more difficult.alot of people go below pitch with each string and then bring it up to correct pitch to help.(i hope i am being clear)a roller nut prevents this by making a frictionless connection.alot of people use them with a wilkinson or similar tremelo instead of a locking nut.
i think what you are talking about with the neck screws is a washer type piece called a neck mounting ferrulle.you just countersink a hole to the same depth as the ferrule so it sits flush.(stewmac.com-hardware)
versatile single coils:emg s,duncan cool rails,hot rails,etc...
everything else is not my department.hope this helps