Mountain Lion Dev Preview upgrade path

Hi! I am thinking about plunking the down the hundred dollars to have access to the mountain lion developer's preview, and I had a few questions I hadn't seen answered elsewhere...

1. When the final public release of 10.8 happens in the summer, will I be able to upgrade organically from the developer's preview (without losing all my data, etc.), or will I have to downgrade to Lion or restore the system first?

2. Actually, I also want to confirm that the dev. preview will install over my current lion and (assuming nothing whacks out) retain my data, yes?

3. If I do get the preview version, will I still have to pay the (likely) $30 for the final version? (I imagine yes.)

Thanks!

I guess my concern is that I don't want to knock myself off the standard upgrade path for good. If the developer preview ultimately updates to a final release that is indistinguishable from the consumer release, then that is great. But would that then get the updates that the standard release gets? And what about eventually updating to 10.9, etc.

I say all this knowing that people who have gone to mountain lion haven't been having much luck rolling back to lion.

My understanding is that people were having difficulty even using time machine, because the ML installation actually altered some of the firmware. No?

Basically, I'm eager to join, but just want to make sure there's a not-overly-convoluted way to get back on the standard ML upgrade path when the time comes. How do all the Devs plan on doing this?