Yes there is Spine support or is it Spriter? I'm pretty sure we have Spine support since Visionaire Studio 4.2.5, but I've not gotten round to testing it out yet & we currently have no documentation on how to use Spine animations / runtime library with Visionaire Studio. Maybe SimonS (one of the engine devs) will be able to provide a bit of help on that.
Yes it's possible to use either or both Key input &/or game pad to control your characters. Lua is recommended for setting up both, but you can use the "key actions" under the Game (cog icon) tab for creating certain actions / events based on which button / key is being pressed or has just been released. By default the left stick is automatically mapped to character walk, so it's plug & play. I don't remember if the right stick is mapped to the cursor or not by default. Again SimonS would be your best bet on information regarding this as I've not had reason to really test it out myself yet.
In regards to Side-scrollers, they are possible as a couple of members on here create them, though they are more point & click based than actual action platformers. VS isn't really geared towards other genres of games besides third & first person point & click games, but that's not to say that other genres can't be made with it, just some of them require various workarounds to make them work as you want them to work.