[quote=@Cyclone]
<Snipped quote by Genni>

Will do!

[@BBeast]

That's a rather thorough analysis, and one that I agree with. I've been over on the nations section and I almost exclusively play nation RPs, and given my experience personally I'm skeptical that the nation section would be any better. It might even be worse. 

I suppose I could control both the good guys and the Keeper.
[/quote]
The Keeper shouldn't need too much effort to control, in my vision. Unless otherwise demanded by the plot the Keeper's role (on-stage, anyway) should be mostly limited to issuing orders and berating/congratulating player characters. This keeps the focus on the players. The 'good guys' might be a bit more work, but controlling the opposition is typically the role of a GM anyway.

[quote]
What I'd like to get your opinions on is whether I should take the time to figure out a plot and iron out the major details before making the interest check, or just make it as the vague idea that we have so far and see what the majority of interested people want. I see benefits to both sides.
[/quote]

While part of me likes to plan ahead, another part of me says that this set-up should make it easy enough to hack in a plot later and in the meantime make do with a few run-of-the-mill missions to get the players warmed up. A cover plot to start with would go along the lines of- 'You are servants of this Keeper. Help him take over the world, crushing the human resistance and enemy Keepers.' You can throw in some complications along the way once you figure those out (don't forget the element of surprise). Since the players don't need an all-encompassing knowledge of the world like previous installments, you have an advantage here.