We use clear lacquar on brass and aluminum
in the shop. Alum's not too bad but brass has to be perfectly clean before spraying on a coat. Any fingerprints will eventually show through.
As for scratching, as long as there is nothing rubbing against them they'll last a long time. Or if you catch a scratch right away, clear fingernail polish is a quick repair.
If they're not coated, and you get some saltwater on them they'll get green and once it's set in it'll be hell trying to get it out. It will actually pit BRASS over time. Bronze
would be more durable but a lot more expensive.
Would like to see your handywork if you can do up a picture sometime......_/)