I've never used Reason, but I find OCaml very easy to set up. This probably depends a lot on how well-supported your editor is. My setup involves:

    sudo apt-get install opam inotify-tools m4
    opam init
    opam switch 4.07.0
    opam install dune merlin ocp-indent

and then add the ocaml layer to my spacemacs config. This gives me auto-indenting, syntax highlighting, type hinting, and my preferred build tool (dune w/ inotify).

FWIW, this was much worse when I did it a couple of years ago. I think the ecosystem has made pretty big strides recently, much of which came from standardizing on dune as the canonical build system.