Thanks for your advice DD.
1. I have the phone audio routed into the aux in of the reface, so if I pull the volume on the YC it also kills the volume of vb3m. Although this solution (local on) does make the rotary lever have 3 postions. So it would be a fine solution if I choose to have audio straight out of phone into an amp.
2. Presets? The reface YC doesn't have any, if that's what you mean.
3. Could do. It does have an expression pedal jack. But then I've lost my swell.
4. I have chosen this one. I have a fader that natively is assigned to vibrato depth so I have mapped that to Leslie and it works fine for 3 speeds. Of course I'd prefer the location of the rotary lever but like you say, you've got to find a way to make it work.
I may go back to the rotary lever choice as it can do slow/fast and I don't often play stop.