Minimum dev environment for plugins...

[micheus]

Is there anything else I need?

dgud, is the best person to answer that, but I think you will need to download the sources anyway if you need to make use of any Wings3D's header file (.hrl).

Does the version of Erlang make a difference?

It's recommended you always use the latest one (currently 19.1.5). Check this Erlang Solutions page in which you can find a proper package for your distro.