A few comments on the schematic:-
- You will never read anything from the rotatory encoder because the arduino inputs go directly to ground.
- There is no pull up on A15 so you will not be able to read that switch state once it is not connected to ground.
- S18 appears to connect the CV to the Gate out, or Gate Out1 - is this correct?
- Not sure why R55 is fitted, it doesn't seem to be doing much.
- You can get + / - 12V if you have an AC output wall wart and half wave rectify the signal for each rail. Although this seems to be a lot of fuss for just one op amp. Maybe you could bias the op amp's ground to 2.5V but I haven't looked at the data sheet to see if that amp can work off +/- 2.5V or a 5V single rail.