I think a calender is a great idea! My wife has done this for Christmas gifts several times, using family pictures of the past year. She has used Snapfish and Shutterfly. They turned out very nice. I don't know how much they cost but she says they offer pre-Christmas sales. She did multiple photos for each month and put individual family member's photos on their birthdays, so I'm sure there are many ways to be creative with this.
I think you should choose the pictures yourself, Mustang. You know the horses personally and surely have a dozen favorites. I think you should also caption each photograph with your insight about the scene and a short story about what is being viewed.
Count me in for one too. I agree with FH that you should autograph them for us. Once you are famous, a signed copy will be worth a fortune!!