Hello! There are no rules on sticking with one metal. I would stick with 2 metals tops though. Either black and silver or black and brass. I would suggest the brass NOT being polished, go with a brushed or antique to give it a more transitional vibe.

Also, while I LOVE shiplap, have you tried considering square panels or bead board on the lower half of your walls? I don't know the style of your home, and if it's a ranch or country then stick with shiplap, but I've been pushing paneling for a lot of my client's lately because shiplap fits only a distinct style and is seeing it's way out as far as trends go. While square paneling and bead board is a very classic and timeless style. Just something to consider! See photo below.