1.) You can upgrade to the latest ROM by following the directions located
HERE which adds a zip program, voice dialing, speeds up transition from landscape to portrait mode, and more.
2.) I would stick with activesync 4.1 since the latest version is still in the BETA stages.
3.) I would first install Magic Button, a task manager that actually close the programs instead of leaving them running as WM5 does by default. I would also install TCPMP which is a media player that can play mpegs. There is also a neat camera program that allows it to be used as a webcam via activsync. You can find that located in the have to haves for your ppc6700 thread.
4.) Im not to sure about bluetooth headsets, but I can suggest you not buy the Moto HS815. Volume on it is crappy.
Hope this helps.
And welcome!
~Mike