[QUOTE=Excal] Velojet, how stable is this plugin?[/QUOTE]@Excal
Test it out!
[QUOTE=Excal]... would this plugin + Photon Cloud be suitable for production quality multiplayer?[/QUOTE] Check the Photon Cloud site
and see what's being done by commercial game developers.
[QUOTE=Excal]Along the same lines, if making a game for multiplayer, is it possible to create it in singleplayer first and then add the plugin and port to multiplayer, or is there a better order that's recommended?[/QUOTE]Design your game from the beginning as a multiplayer - retrofitting a single player game is not a recommended approach.