Try silver solder for your joint, there are several melting points/grades available. This joining process cleans up no problem, if you need further advice come back to me.
The basic polishing process is pretty straight forward.
If you have a lot of corrosion I think ideally you might want to remove the tarnish and oxidation by chemcial means; I'd use 50% Hyrdrochloric Acid.
Use a pleated cotton buff to buff the brass with a tripoli compound to do the "dirty work" and finish the color buffing with a chrome rouge or jeweler's rouge to obtain a high color bright brass finish. All of these materials are available with polishing and buffing distributors in your area.
The protective coating over the buffed finish ... consider
