Definitely a trial run would be in order.
Movie/book things would be more exposure but would mean more chance of us not doing it "right" though... if it's something of our own conception then at least we don't have anything to live up to and nobody can sit there going "ohh, they haven't done that right, it should be 3 blocks higher and to the left" :P I know I've seen things done and gone "ohh, it's pretty good, but they should have done XYZ", whereas I don't think I've ever had that thought when looking at something done that's not a recognisable thing.
Though Minas Tirith, or Hoth battle scene would be awesome (though both already done)... there are so many cool things out there just begging to be replicated in minecraft.
We could always video our practice one too... if it turns out too crappy to publish then we don't publish... if it turns out ok, we pop it on the channel anyway and say it's a test and link to the eventual proper one.
Recording would be better than screenshots IMO as you dont miss anything.
When we were talking about screen shots, we were talking about a minecraft mod that automatically takes a screenshot every second or 2 (or how often you set it up)... so when you combine those in an editor, you get a time lapse video..... which is apparently lower file size than the equivalent made as a video recording.
I've bought playclaw (like fraps) and yesterday practised making a vid of my place - editing it with movie maker (which is in my temple thread in the gallery)..... so I'm now familiar with how that all works, and with the edited video the file size dropped dramatically (as in from 641mb for a 3:25min file without audio to 111mb for a 3:45min file with music), with no discernible difference in quality from the original.... so given that, I agree, videoing rather than screenshotting would be the better way to go, since we should be able to do it and keep the filesize low enough (hopefully).