I myself haven't used Krfb.. I've used Remmina - its in Lite Software or Synaptic.. Its more like Remote Desktop/VNC (it does not lock the screen like a RDP session)..
I've never had to start something on the remote system or "allow" like a remote assistance...
Works well with RDP too; Linux to Windows...
For auto-start may want to try:
Menu, Settings, Session and Startup, Application Autostart tab, click on the Add button.
I'm not in front of my system but that maybe be close
... If that's suitable for KRFB??