Ok, first check out
this interactive guide to three point lighting.
Key light: Main light source that illuminates your subjects.
Back light: Light behind your subjects sometimes reffered to as an edge light that helps add dimension and break them up from the background.
A low key light would mean it isnt very strong, just enough to fill in a little so you can see them but they are someowhat dark. A strong backlight means they have a hard "edge" of light helping silouhette them so you can see them seperate from the background. It will also illuminate fog if you have that in the scene.
As to "floods" he is reffering to flood lights. In the actual video the used lights called HMI's which are large lights that register the same color as daylight on film. These are what are used to create the blueish night/moonlight look for night scenes in movies. They are very expensive even to rent so I would suggest simple dual head halogen work lamps from Home Depot. They are 1000w so they toss a descent amount of light (not nearly as much as an HMI though) and they register white on video so that is good. The trouble is they are about $30 a pop and you will need quite a few for a scene that large.
Here is another suggestion. Since it is so large and you have limited resources you might want to shoot day for night on that scene.
Wait till a time of day when the sun is behind your actors (creating a large backlight) close up your iris and/or increase shutter speed to make it a bit darker. Then in post bring down the levels a little, tint it blue and your done. It wont look exactly like night but if you shoot all of it this way it will create a convincing enough effect for what you are doing. Good luck.
R. Michael
"Luck, is when opportunity, meets preperation." "There are 3 sides to every story. Yours, mine, and the truth, and none of us are lying" -Robert Evans
Tizzy Entertainment "Redemption" Hi-Def trailer