Depends on how often you intend to use it. Figure about 1-1.5 ounces per car, so the 16.9 ounce bottle will do one coat on about 12-15 normal size sedans. If you need more than that, save on shipping and get the bigger bottle.
I don't know....I have done about 12 cars with AIO and I still have more than 2/3 of my AIO left. I think 1 oz is a lot of product. Same with SG....I have probably done 20 or more coats on various cars, and it's maybe down a fifth.