You may have already known all this since many of you are much smarter than I am, but just in case…
1. You can use a zoom lens while in video mode, but it has to be a fixed (not variable) aperture lens so that the exposure doesn’t change while you record.
2. Canon’s ALO (Auto Lighting Optimizer) setting is designed to deal with high contrast situations. But in Manual mode it looks crappy. So Canon has designed a custom option that allows you to turn off ALO in all but P, TV and AV modes.
3. When looking at images on the LCD screen you can overlay any of three grid display options (3×3, 6×4 or 3×3+diag) to check the composition of images.