Hi
Interesting Project.... Whatever i not fully understand in case of translation.
Best way to discuss this is our DISCORD
https://discord.gg/99vHbK7
Join and talk to me there. Then i can directly support you !
About Questions....
MF support Poti meanwhile. (Since 2 Years i think)
To set 3 Pots you need 3x Data and shared 1x GRD and 1x 5V .
Electrical i´m not sure if you can use a external 5v ... Maybe if the External device is combined with the GRD of the Arduino where pots are set.... But 100% sure pots work fine if both (5v and GRD) comes form the Arduino where you also set the Potis.
If you like to controll "different" things then you need something like a Mode Selector. (Your 4 Buttons). Those will need 4 Pins and one shared GRD.
We could also build this by 1 Pin as a toggle.... So a Button that toggle between mode 0,1,2,3,0,1,2,3, and so on with every press. ( To reduce number of wires as you expect).
The final logic is done in MF ....
You say there ( PRecondition and/or Placeholder logics) that your 3 Potis should do XXXX in Mode0..... YYYY in Mode1 and so on.