How accomplished are you with in-hand skills? Tricks are only an extension of in-hand training, in my experience.
Honestly, teaching horses tricks is really the same as teaching a dog. Cause a behavior, reward it. Cause the behavior with the support of a cue, then reward it. Use the cue, reinforce it, reward it. Once you have some "try", you can build and mold a behavior into what you want it to look like. A smile is just reaching for a piece of food with the lip. Once they understand it's the lip up that's the desired behavior, they'll begin to offer it.
I'd be very cautious of a "high 5" type of movement. I do have my horses wave and Spanish walk, but I do that beside them and not to target me with their hooves.
Another extremely important thing to keep in mind when training for tricks is having an "off switch". Especially when you're doing movement tricks (if you want to go there) like the rear for example. I train a very firm "whoa" before I teach any movement tricks.
Clicker training is great, if your horses bridge to that. But it's absolutely not necessary for success. A clicker is not a remote control. A clicker is an articulation of the right behavior or engagement. It's saying they're doing the correct thing, or on the right track. You can just as easily accomplish that with your voice and enthusiasm. The benefit of the clicker is you can articulate a very specific moment whereas your verbal and body cue may take longer to communicate.
Anyways, best wishes! I think you've got a great idea!