For the document, what you put into it really depends on what kind of designer you are. There are numerous types of design documents. Some people like to have every last detail planned out from the start, and others like to keep things very vague. Both methods have their strengths, and weaknesses.
Since it sounds like you're going for a proof-of-concept, and not a finished product, you don't need to plan for things like game elements and game progression.
At the least, though, you should cover:
-Razor / Focus statement(s)
As for the disconnect: You don't have direct control in that type of game.
It can get incredibly tiresome planning actions in advance, and then watching the action take place. How long it takes for the disconnect to start grating on you depends on the ratio of planning to watching, number of possible actions, polish, and (most importantly) the audience.
I have little patience for it, myself, though I imagine most people would handle it better than I do.