When do I need to white balance the camera?
Best practice dictates that cameras should be white balanced every time a lighting setup changes. Camera presets may be used for safety/to save time, but can never be as accurate as manual setting!

What's the difference between Blue and Green screen Chromakey?
Historically, red, green and blue channels have all been used for matte work, but blue has been favored for several reasons. Blue is the complementary colour to flesh tone, and since the most common colour in most scenes is flesh tone, the opposite color is the logical choice to avoid conflicts. Historically, cameras and film have been most sensitive to blue light, although this is less true today. Green has it's own advantages, beyond the obvious one of greater flexibility with blue foreground objects. Green paint has greater reflectance than blue paint which can make matting easier. Also, video cameras are usually most sensitive in the green channel, and often have the best resolution and detail in that channel. A disadvantage is that green spill is almost always objectionable and obvious even in small amounts, wheras blue can sometimes slip by unnoticed.

What's the difference between f-Stops and T-Stops?
f-stops are calculated aperture openings; the “f” refers to a fraction of the focal length: f/2 means the aperture diameter is 1/2 the focal length. F-stops are used on still and video lenses, and are the basis for depth-of-field calculations. T-stops are f-stops which are adjusted for lens losses; they are measured settings giving the same exposure as a “perfect” lens would at the calculated f-stop. Prime lenses normally have f-stops and T-stops that are nearly identical, but complex, long zooms may have T-stops that are as much as a full stop slower than their f-stops, due to internal reflections and absorptions. T-stops are normally used by cinematographers, who have traditionally not had through-the-lens metering to compensate for any lens-induced light losses. T-stops allow swapping between widely differing lenses while keeping the exposure constant, without having to calibrate one’s light meter for each and every lens separately.