Here is a link that describes caring for a western show saddle. You can use many things on silver, including the spray they mention, various commercially made creams, WHITE toothpaste, or a past made from baking soda and water. The most important thing to have if you expect to do lots of silver is terrycloth, and lots of it. You use it to clean, and then use a clean piece to polish. I guarantee that your terrycloth will be black, so don't use good towels, LOL. Some headstalls and breastcollars, and to a lesser extent reins, have rawhide and silver. Make sure you don't let your silver polish get on the rawhide or the leather. Here is a link that describes cleaning rawhide. Care and Cleaning
A lot of saddles are tooled, which can make them difficult to clean. Not terrible, but compared to an English saddle, not so easy either. If you polish belt buckles, be aware that a damaged finish on goldtoned areas should not be polished with many cleaners. I had an award buckle that I didn't realize had a damaged finish, and I polished the gold right off.
Leather cleaning supplies, which it sounds like you've got a grip on. I would add a soft brush or something for deeply tooled leather.
Silver polish, either store bought or home made, and plenty of terry cloths. I like the cheap bar rags you can get at Wal-Mart. Last time I bought them I got 20 for $6 or something.
Elbow grease and lots of helpers! It sounds like a wonderful idea, and I hope you all raise a lot of money. Good luck!