There are some PC apps that will work with 720p50, such as one from Cineform I believe, but if you are using FCP, then 1080i50 is it, or the most official way at least.
You can transfer clips directly from the camera through FireWire, yes, or you can put the cards into a G4 laptop that has a PC Card slot. Other various devices may or not work. I personally have not tried anything else, other than the official Panasonic P2 5 slot USB device.