Most of your questions are beyond my knowledge of NFS, so I'm not going to be able to spot problems in your config or warn you about potential problems. Maybe someone else can.
For NFSv3, the only concern I've heard about it in the context of ActiveMQ is that its locking mechanisms don't allow it to be used for a filesystem locker. Since you're not doing that, I think you'd be OK using it for the data files themselves, but again, this is not an area with which I have any personal experience. Tim
