Getting over there can be a royal pain
I took my DD horseback riding one year when we stayed at the Poly. We took the boat to MK then the Ft Wilderness boat. Once you get there you have to take the internal bus. It was very time consuming and a little confusing
Unfortunately the concierge at the Poly gave me some bad advice
Depending on where you are staying, I would say take a bus to MK (or any park) then take the Ft Wilderness bus. That should be the easiest way other than taking a Taxi--which would be the quickest & easiest way. Once you get to Ft Wilderness, just ask a CM which way to go from there. Busses start running an hour or so before park openings (someone else can tell you for sure, but I think they start at 7 from the resorts, not sure at all about DTD)
The trail ride was fun, the horses were very good (well behaved/trained). Horseback riding skills are unecessary. You do have to have closed shoes (gym shoes or boots) absolutely no sandals allowed. Jeans are recommended. If you are bringing a small child, make sure to check out the age/height requirements. They are very strict about it and will not allow any exceptions.
Have fun and keep an eye out for armadillos, deer, and all sorts of other creatures