The keyboard layout editor is okay for getting the basic notion across as a very first step in an IC thread in the Interest Check forum here. But if there is any meaningful interest you will almost immediately get requests for CG renders.
The most time-consuming and exhausting part of the development process, IMO, is achieving community consensus on kit composition. Once you have settled on the kits, it's time to put up a Massdrop poll. Massdrop still does not have a formal keyset proposal protocol for designers to follow, so at this time you have to just put your keyset renders up wherever you can and hope you attract the attention of what I call the Massdrop Makers Cabal. Alternatively, you might attract the attention of one of the smaller, independent group buy agents.
Generally speaking, you don't have to contact the manufacturer yourself for anything unless you have technical questions regarding your design, like custom colors or legends.
