Wick, before you try to glue brass to wood, you want to rough up the bottom surface with fairly rough sandpaper. Then, use either epoxy or ACC (Krazy Glue) as these are fairly weatherproof. Escutcheon pins are better yet.
It's hard to describe what brass looks like after a coat of varnish. Before you decide on this though, run down to your friendly local hobby shop and buy a small piece of K&S brass or use a scrap and put a coat of varnish on it. It's kind of hard to describe, but it does not look as good as with a coat of lacquer. The lacquer will not last forever in the weather but is should last a good long time. It will stay clearer and more translucent than with the varnish.