Here's something to think about...
I work for a large steel fab corp. I just went out in the plant and asked the head foreman (who has a waterfall in his pool) his opinion on the grade of SS that should be used. He said his advice would be to go with aluminum. It will save you a LOT of money and there is no risk of it ever rusting. He told me that SS is not foolproof, it can actually rust over time, especially in a chemical environment, or if it gets the surface scratched up. The majority of SS is plated, not solid through and through. (I learned something there. lol) If the business near you works with stainless, they most likely have the ability to weld aluminum also.
I can't wait to see your pictures of the finished product!