So I've done a bit more work on the point control in that it will now actually throw an OO9 gauge point. This is achieved by attaching the servo arm to the point tie bar using some 0.5mm diameter piano wire running through some 2mm diameter aluminium tubing (both from Albion Alloys) to keep it in place; i.e. a proper wire-in-tube system.
Everything is currently just held down with double sided tape but that seems to hold well enough for experimentation. I could have glued the point down though as I won't be using it on the layout having damaged it beyond repair when soldering on the wires (one of the sleepers is so buckled that the switch rails don't line up so things derail) but it works for this purpose. I found using the second hole from the end of the servo arm and a rotation of 10 degrees was enough to nicely throw the point. The calibration was a bit hit and miss though so I need to work on the software on the Arduino to make that a bit more user friendly but so far I'm happy with how it is all working. If I can figure out how, I might slow down the action to be a bit more prototypical, although that might be tricky given that I'm still relying on the spring in the points to help complete the throw.
Next up will be checking that I've understood the frog switching wiring correctly by attaching the three wires from the point to the relay and checking for the expected power flow through the point.