The first improvement I’d work on making after replicating the existing system (i.e. sonar sensor for current ride height and servo for actuation only) is improving the algorithm. Specifically, the gearing on the UFO is setup to handle waves as well as possible at a slight top speed cost, but with the electronic system it’s easy to automatically adjust gearing. What you want to try is taking lift off the flap faster when ride height gets too high, adding it back faster when boat gets near/in the water and keeping the flap close to neutral at a constant gearing at your desired ride height. someone has already set this up mechanically in a moth: https://avalonsails.com.au/blog/2018/3/14/latest-update-on-the-bugs-cam. The ride height adjusted gearing should make the boat easier to foil and less likely to ventilate. It can also improve top speed by reducing flap actuation and associated drag when you’re stably foiling at your desired ride height.
My second thought is that boat speed sensors will be a pain, because gps will not give accurate boat speed if there’s significant current. That’s why I think you focus on what you can do to improve the system without boat speed as an input before you add the additional sensors. Paddle wheels are out for speed through the water, because they’re a pain and where do you put it. That leaves ultrasonic speed sensors, but they also need to be in the water, so where do you put it. Best place is probably the mainfoil. You’ll definitely need to find a sensor way smaller than what I’ve seen on keelboats and find a faired way of incorporating it. And You’ll need a second prototype mainfoil to incorporate the sensor and fairing, while still having a one-design UFO readily available. Anyway, my two cents is to get started under the assumption you won’t know boat speed and only incorporate boat speed later. improvements can be made without boat speed data for sure.