Jim:
I always dismount for oncoming traffic, be it horse, pedestrian or other cyclist.

I generally don't feel comfortable alerting folks I'm overtaking;  I'll say, "on your left/right," when it seems appropriate.

I'm usually uncertain what to do when overtaking a horse/rider.  I don't have any recallable experience in this encounter.

Good luck to your project.  Its needed.

We need to add your conclusions to the  club's next issue of the trails and routes map --with a notation that states that the rules are a consensus of all users.

Now, what about motorcycles?

thanks for your initiative

bob