Stainless steel or carbon steel??

Stainless is harder to distress and age but it has a distinct industrial look when done right.
Stainless also has near square (sharp) edges/corners which is a different detail/look.

Iron would be my choice and if we are going for an aged or distressed appearance there are a number of ways to achieve that all of which produce different results.

It can be painted to match the black iron on the fireplace or any color under the rainbow.
We can use the variety of paints on the market that produce hammered metal appearance or rustic weathered.
I am not super thrilled about most of the available products - They dont look natural.

We can do a weathered/aged and distressed look the old fashioned way (I can tell you my recipe…..but...) that produces a more natural occurring range of colors and textures.

When I am doing this I like to use the cheaper carbon steel from China – It’s structurally sound but the carbon content varies through the steel tube which yields a random rustic inclusion of color and cool textures.

Or rjust paint to match the firplace

Carbon steel types/shapes typically have a larger radius corner then stainless because it is “cold roled”
This is an important detail to remember in the design.

The island is definitely taken a turn toward custom.
If you settle on wood offered by a manufacture or painted I think we can still design around some standard cabinet sizes and modify them to tie it all together.
If we are sourcing our own handpicked barn wood or salvaged reclaimed lumber for finished backs and end panels and drawer faces we may as well just build the whole thing ourselves.