Just some quick suggestions about Steemmarines lore @malicered
Let the founding chapter be Iron Hands.
Let the Steem Marines have a deep connection to the Adeptus Mechanicus.
Let their homeworld be one of technological advancement.
Try to implement blockchains, IOT, AI and other themes into their tech and their culture. Very very heretical stuff. This is why there needs to be a big fight against the Inquisition in the history of the Steem Marines chapter. So, let the Ordo Hereticus consider the Steem marines heretics.
Let them have a twisted admiration for Necrons.
just some thoughts I came up with and I think would be cool and make the chapter unique.