By “official usage centric documentation”, are you referring to the official OCaml docs? Or something else?
Also, could you provide some examples or references about the kind of information you would like to see in the docs, please?
Yes, but you can skip the --dev-repo flag, as a direct commit is being passed to opam pin.
Unfortunately pinning is the only way at the moment. Hopefully Dune 3.8 will be released soon 
and we can publish reactjs-jsx-ppx and melange packages in opam, so having to pin specific packages when working on Melange projects becomes a thing of the past.