I'm using the TWX Java client SDK to communicate with ThingWorx by extending ConnectedThingClient. I would appreciate answers to any of the following questions:
Yes we support WSS, I believe the documentation in the Portal should give guidance on that, or else you can look at some of the docs included with some of the SDKs.
By default they should be setup to connect WSS I believe.
I'm uncertain about the second part of your question. I do believe simultaneous requests should be possible.