The expression pedal has been working to control volume since version 4.3.1 has come out, it is currently available on WiFi
Decay was re-implemented in beta 5.0.0
The EXP setup is also much nicer looking in 5.0.0 with its own settings page and design
This is currently not possible and may not be possible for the near future
The decay rate currently can only be changed by saving the song in 5.0.0