To start with the conventional tuning for a 4 strings EADG & to begin to experiment altered tunings in a way of "sounding ala Michael" according to a minimal progression through the difficulties, i would suggest :
E
G D
G
D A
D G
E
A D
A
E A
E G
I am not intended to substitute Michael's explanations here but with this
simple set of one altered string per set, you can freely apply the
Sequencer* Tapping style which is to my sense his main concept & his touch (sounds like synthesizer pads).
A fretboard analysis of all fundamentals/
open strings/octaves for a given pitch note will give an insight of what is possible (focusing on 4th intervals to the right hand).
I mainly venerate two Musicians (not technicians) : Vangelis & Manring.
Greetings to him from France.
*
PS : Michael, do you play Keyboards & further more do you write your Themes with them ?