Yes, it is. A lot of effort was put into this feature. We cannot guaranty a 100% compability, but it should be very close.
You should always use the latest version that is available, because it offers the best performance and bugfixes.
Yes, it is. But you can install different JRE versions in parallel, just make sure BattleDuel uses the correct one.
No. And there are no plans to release it in the near future.
Well, this depends on the feedback we get from this Java port.
BattleDuel has been developed and tested on different Windows, Linux and Apple OSX systems and should work without problems.