I managed to sneak out last night and test out my boost issue on the primary turbo.
I was almost certain I had fixed it but unfortunately not! I still have only 0.1 Bar boost coming in on full load, however the car feels so much smoother, that nasty vacuum leak was definitely causing an issue as it's now smooth as butter through the gears and low RPM and boost comes in really hard with the second turbo.
After doing hours of research last night I've narrowed it down to the following
Knicked or damaged vacuum line to pre control actuator not allowing wastegate to open/close
Wastegate actuator control road circlip popped off and rod is not attached to actuator causing flap to stay open and loose pressure
Apparently there are vacuum hoses near the vacuum chamber that have restrictor pills in them, I replaced these a while ago with those lumo green ones I had lying around as they were cracking but after researching it seems if you have too much pressure on those lines = less boost and restriction = more boost. I definitely don't have the restrictor pills anymore if they were inside the old lines as I would have thrown them away but I have another RX7 FD3S to steal it from! Lucky me.
Damaged charge control valve - Easy, I have one on the other FD to test.
Oh, it's not a boost leak as the turbos share a common Y pipe. If there was a leak it would affect the second turbo too and not allow the pre control actuator to work.
Anyway, back to the drawing board. I'm in no rush to sort this out so will probably mess around on the weekend again.