Verizon and UTStarcom issued an update in July 2006 that allowed simultaneous use of the phone and WiFi. Phones sold after that date have the update already installed. So you don't need to edit the registry anymore .
If you want to sync with your Mac, you'll need Missing Sync from markspace.com (PPC-Mac syncing software). The EVDO Treo 700p syncs to both Mac and Windows, but sadly it lacks WiFi. So the XV6700 sounds like a better bet for your needs.
The phone will sync with Exchange for such things as calendar and contacts, yes.