These are lovely images! I'm no expert but if it were my gig I'd shoot all the person/horse portraits and posed horse portraits with a standard portrait flash/strobe set-up - meaning two lights, one key and one fill in a 3 or 4:1 power ratio. Mixing natural and flash lighting can be tricky but since most of the portrait shots are outside it would be important to do whatever it takes to keep the sun off of the face since that's what produces the overexposed facial areas juxtaposed against very harsh and dark shadows - always a portrait killer.

I may have missed it but I don't think you mentioned what metering mode you're using. Again, I'm no expert but my inclination would be to use spot metering linked to whatever focus point I thought would be most useful given the predominant direction of the action, hoping to get into a rhythm where no matter what else was happening I'd likely have the horse's eye in focus and exposed correctly.

It seemed counter-intuitive to me at first but de-linking exposure and focus (by assigning focus to a convenient button and leaving exposure to a half press of the shutter button) greatly facilitates action shooting. It took me just a few minutes to become convinced of the benefits once I resolved to try it. It's not something one needs in the studio or for static tripod landscape shots, but definitely something to use for all sports and action shots.

Mostly I just wanted to say how much I like your beautiful images above.