1) How many sectors do you usually fly per day? How many hours does this equate to?
Somewhere between 2 and 6. The two sectors can be as little as 1:20h block time each way (2:40h day) to nearly 4:00h each way (8:00h day). The 6 sectors tend to be around 1:10h each (7:00h day). Though most of the time you'll be doing 4 sectors.
2) How many people does it take to crew the 737-800?
1 Capt; 1 F/o; 1 Purser; 3 Juniors.
Though I have flown with 3 pilots and 6 crew, lots of training that day!
3) How many crews do you need per aircraft?
I think we try to have around 4 Capts and F/os per a/c, though I stand to be corrected on that. I have no idea about the crew.