Definitely add pictures of your stalls and the whole barn. I find it rather suspicious if people don't post those. I don't want it to turn out that they are wire cages (figuratively speaking). And prices. Also, if you could add a little map from google or wherever that you can add so people can click on it and get directions to your place that is always very helpful.
Make sure its a clean and organized layout (Believe it or not, but I saw a website where they had a black background and black text! The only way you could read anything was when you marked the text...)
For the summer camp, add dates or at least durations, prices, pictures and descriptions of activities. Maybe you can have someone write a journal while there and add it? That isn't necessary, but it would definitely be a nice touch.
Also make sure your boarders are ok with being presented on the site. Just to be on the safe side.
You can also write hours of "operation", meaning hours at which people can come and see their horses. Just so you don't have someone showing up at 1am thinking their burglars
It also give speople an idea of when to come to check out the barn.
Speaking of which, define what boarding includes, what requirements the boarders have to meet (health certificate...), things like that.
When I think of more I'll let you know