The Crossroads of the Aether
Actually you are the first steamship pirate I have run across here. As a pirate, most any hat you choose to wear will work just fine. If your back story has you as a member of the losings side's navy in a war, you might want to research naval hats used during that war. The old tan trench coat should work just fine. Accessories are the key in both cases; pick something nautical or a creature of the sea that interests you, and find/make brass items patterned after your choice(s) to embelish your hat and coat.
I would think a high, peaked cap works well, something Russian miliyary surplus.
You will also need to start looking for an appropriate holster/lanyard for your Schofield Russian revolver or perhaps a Le Mat. Both are very distinctive and completely appropriate for such an individualistic persona.
a cannon that pops out of a top hat and fires...hmmm...a taller top hat...hmmm...an abe lincoln would be tall enough me thinks
ah yes...a gun on a disappearing recoil mechanism...it pops out...fires...and recoils back in for reloading...excellent idea s.d.