People like color and they like shine. That means mica clays for the shimmer, powders where applicable, foils where applicable, and glazing where applicable. I'd stick with the horse theme since you know that works with the crowd and seems to be appropriate for the event. In addition to "literal" horse, don't forget to suggest horse with general forms, shapes, and even things that suggest movement.
Yes you are ready! Don't doubt that you are. You have good design insticts so don't let your analytic side of the brain over-think it.
Lori is right - mokume gane and swirlies are always hits, especially if there is plenty of color.
Depending on how much lead time you have, you might want to check out www.madaboutmolds.com to see if there is a horse mold which you find appealing. I put a gold mica-powder-covered molded dolphin on a solid black oval in the landscape orientation and it's simple, effective, and easy to replicate.
Make sure you hand out business cards so people can contact you to buy more later. Plus have them sign up for a contact list so you can email them when you have new pieces of interest. Take a few samples of things that are not horse related - Mother's Day is right around the corner!
As for ART show rather than CRAFT show - pay attention to how you finish off the pieces to make sure they are well sanded, etc. Great workmanship and attention to details will make a difference. ART usually means one of a kind rather than a bunch of the same thing, also 2-3 or even six of a "memento" piece is probably a good idea.
Check out Lisa Pavelka's site. She has done very well making her themed eggs in quantity for special events and it has been good for her business.