Yay!
This is tricky to answer, because the recent MSTs have had maybe 15 people show up. However, the push south + the new group of locals who will show up may increase that number. High or low, who knows. I can't really tell, so instead the safest bet for me is to get as many set-ups as possible to run it smoothly. I'd rather go overkill on the set-ups and not risk a bad set-up : players ratio
Well, there's no guarantee that low tier will even be ran (Low tier is a slow running tournament, if a bunch of people show up it'd be a waste of time to run it, and we could run some other warm-up tournament in its stead.). Again, I've no clue how many people are going to show due to the potentially high local player showing, so unfortunately I can't estimate when doubles and singles will start.
I run weekly tournaments at a local card store (J & R Cards, we've ran MSTs there before), and 8 is about the number of people that show up. We manage fine on 1 set-up, but thats mostly because we run a single elimination tournament. If you were to do double I'd at least suggest 2 or 3 set-ups. If, since you have a low number, you wanted to run a swiss format tournament (Everyone plays everyone once, top half (By record) enter a double elimination bracket), I'd consider going for the 4th set-up.
EDIT: If anyone was interested, here's the thread for MST11 on the Maiden Games forums
http://hexcaliber.proboards38.com/index.cgi?board=general&action=display&thread=1174025100