DIY - WAH VOLUME EXPRESSION 3 IN 1 Pedal - HELP NEEDED! ;)

[MBMods]

Hi folks, 
First post for me, be gentle 🙈

I'm converting my Vox Big Bad Wah Pedal to work as a multifunction pedal in my rig. 
I am using an ES-8 in my rig so I wanted to create the pedal to maximise functionality whilst occupying no extra space on my board.

THE DESIGN
the idea was to have the original wah circuit,  a separate volume circuit (with seperate input and output jacks)  and a separate expression pedal (with seperate trs Jack input) all work off the same potentiometer.
Wah on and off will be under pedal switch. When off this will cut over to another switch which I'll install to switch between volume and expression  modes, both of which can be bypassed straight to wah mode again using under pedal switch again.
(I'm not overly fussed about the POT shape (linear... etc)  - this was more of a fun project to see if it can be done).

THE REALITY
I drew up some wiring ideas and tried a couple to see what worked and failed and have now reached an impasse at the last hurdle. (Schematics attached - apologies for quality,  hand drawn on my note 9 at 11pm)

I have already drilled the holes in for the jacks, replaced original footswitch with a 4dpt and added a second one for volume and expression switch. I have wired as diagram attached and all three circuits work independently - HOORAY! 😅

THE STRUGGLES
The only issues I face are:
1. I'm getting a hum from the expression pedal (i assume from the voltage from Boss ES-8 EXP in port, but not sure how to reduce that hum)
2. Finding a way to have the wah circuit enabled via first 4pdt switch and the other 4pdt switch set towards the volume circuit (to allow circuits to work in series and cut to and from the wah circuit to volume circuit via the first 4pdt switch.  I have a bypass setup for volume circuit when 2nd 4pdt switches to expression pedal but don't have enough extra poles to wire one in on the same switch as the wah (unless there's a better way of wiring these?)

Any clues if there's a better way to wire these? And any way to reduce the hum from expression circuit)

Many thanks
MBMods