so many questions haha i dont have time but i know the answers so ill try and be brief.
Steam features are partially available via the Greenworks plugin. Search the forums for it.
Construct 2 has a Wii U export option, but you need to be fully aware of the limitations of the nintendo hardware since its using a web framework (which is why it works with c2). You dont have the full 'power' of the wii u, so testing your game from the ground up on wii u is recommended. You need to submit your game to nintendo to get approved as a nintendo wii u developer, then once that happens, Scirra sends you a plugin to use to build in wii u features.
Piracy... is piracy. you wont stop it and theres no protection in c2. Node webkit builds your game as an executable .exe (windows) or .app (mac) file. ANyone can copy that and play it. releasing through steam signs the executable so at least its tied to the users account and they must be logged in to play, but thats skirtable.
dont worry about your game being pirated. wasted effort unless you got a team of people to pay salaries to and your game is missing out on tens of thousands of dollars because of piracy. just get it out there.