Sounds great Chris! If I were you, I'd outine this brief as is to the players, no more. Leave lots and lots of blanks to 'question out' during chargen, then start the game with an action scene building on the setting established during all those questions...
Perhaps the party is holed up in the heart of a dungeon they had looted, beset on all sides by encroaching denizens of the underdark and an ambitious band of cut-throat adventurers with greater resources at their disposal, hell bent on taking the prizes the players have garnered.
Or post shipwreck, bereft of their gear, whilst scouring the beach for their possessions, the players sorrounded by natives (monsters?) believing them to be gods sent amongst them to be judged (or sacrificed).
That sort of thing. The 'custom moves' you are looking for can simply be variations on your goto move of defy danger (for now), after the first session, when you have a few more solid dangers to develop, you can create some specific custom moves.
Sounds like a great adventure setting in the making!