hey +1 on the gunsmithing area from page 2. needs to be well-ventilated. if possible, even have a 'hood' for spraying all the solvents while cleaning guns. room for lots of tools and work benches.
another possible addition is a reloading area. if you sell/stock powder and primers, you may want to make sure you can do so safely and follow any special regulations. further, you may consider offering classes on reloading, just like classes on shooting and safety. the additional requirement for the reloading classes, which are quite popular in my experience, is that you'll need a space to permanently mount some presses and other gear.
or maybe something like a large, heavy, square bench with presses on 4 sides, that you can put in the retail space most of the time, but wheel into the classroom when you need it.
edit: one other thing... if you plan to do much mail order/internet sales then you might consider quite a bit of back-office, order-fulfillment space. heck, maybe even a loading dock if you're doing a lot of ammo or component sales. you'll need space to pack and ship all that stuff, not to mention receiving it.