Hiya Papabear,
I can't answer all the questions to any great detail (but I know there's plenty around who can)
I'd suggest the best way to look after it all is to make sure you keep your grooves clean and your o-ring greased. This all helps keeping the seal in good condition and stops a nasty flood! :S
I guess they sell a weight as it's probably positively buoyant without it. I don't really know the pros and cons of such a weight. The camera I had didn't have a weight and it was perfectly fine to use.
Hope that helps a bit and gets the thread rolling
Enjoy your photography!