The David one is really where I'd like to start.
In my sorta... "vision" for it, we would have a prologue that wouldn't be a full episode length, more like five to ten minutes or so, and then a week or so later we would release the actual first episode.
This is how I think the prologue should go:
We start with him narrating and showing him crawling around on the rocks. Telling us his view on being turned into a rat stuck on an island, etc. The narration would probably end up sounding like he's become psychotic, which he has, but more like a calm, contained psychotic. Then Crayak comes to him and gives him back the power to morph. (I need to flesh this bit out some more, because I don't exactly know what sort of deal they would strike, though I know they struck one, if I remember correctly. Probably something like the Animorphs' heads on a platter) It ends (que dramatic music) with David on the beach with, like... a sunsetty backdrop, walking towards the "camera".
That last shot would also make for a good "poster".
As for the resetting of the game, I think it makes more sense to wait until the end of the series and then have that explained, maybe their "real" futures being explained as well.