There is an entire category dedicated to Cleaning and Preservation. (You'd have to go to the HOME button and then scroll down to that particular category.) There you'll find your answers to cleaning all sorts of things. For brass, if it isn't too encrusted, you can use a common product called Brass-O.
Opinions differ as to which items and under which circumstances something should be cleaned with chemical or mechanical means. If you intend to clean things with anything other than soap and water, you might decrease the value of those things. It's nice to clean things, however, for one's own personal collection if you don't intend to sell them. Collectors are picky and don't like to buy things that have been cleaned and/or polished. There are exceptions to be sure, but not many.
Once the rust has been removed from relics (if you choose to do that), you can use any number of preservatives and paints. My choice is stove black because it's easy to apply and produces a uniform and satiny surface...a black surface.
