In regards to fan films I would expand rule number 1 a bit: I would say don't even begin to plan to shoot until you've got a final, polished script. How do you know it's "final" and "polished"? Well, I've got my tongue just a bit in my cheek, but really if you were taking a long car trip on business would you start before you had a route mapped out? You might still have to take detours along the way because of road conditions, weather or mechanical problems, but at least you know where you're trying to end up. Every re-write of the script should reveal previously unforeseen problems either in plot, dialogue and/or character and each of those problems dealt with before shooting starts results in enormous time savers when you start shooting.
To stretch the point even further, you might compare it to a battle plan. I remember a General once saying that no battle plan survives the first shot. However, he added, that's not the point. You want a plan that's quickly adaptable to realities, that gives you multiple options.
While I have great respect for the Exeter crew, with the hints Maurice has given out about the problems involved in putting together the missing act IV, I can't help but think there was a fundamental problem with the script and/or planning in the front end that could have been avoided.
Sure it's hard, but that's why so many fan projects are started and so few are finished. That's also why I'll raise a glass to anyone who can actually get a project released.