For a first car, you certainly have a choice automobile. Welcome to the BMW family, and we are a family. You seem to be on the right track; i.e., avoid car washes and stick to hand washing, use the recommended minimum 91 octange gas, etc.
Since you have a convertible, there are a couple extra things you can do to keep the top looking as new as possible. For instance, as soon as possible, remove any dirt from it. For example, bird droppings are especially harmful to cloth convertible tops because they're so acidic. You'd be wise to carry some type of cleaner and microfiber cloth with you just in case. Don't ever fold the top when it's wet, or when it's too cold out (I think there's guidance in the owner's manual about the latter point).
Other than those points, there isn't really anything "special" you have to do to keep the car looking and functioning as new as possible. BMW includes free maintenance for the life of the B2B warranty, so you don't really have to worry about that aspect. Most of all, enjoy the new ride and post pics when you can stop driving long enough!