This is all great advice!

2 cameras for interviews are very helpful. A discreet cough before each take helps when you come to sync sound later.

On the subject of B-roll though, instead of thinking interviews + B-roll all the time (tired of seeing it?), try to film actual sequences of sync footage that speak for themselves and can stand alone in the edit in place of just more talking heads. Or get your interviewee to talk to you whilst they are doing something, and make sure to film coverage of the action. Not always possible and it's more work, but the results are more interesting.

Can't remember where I came across this but one technique I find very useful with Keylight is as follows:

1. Duplicate the foreground layer
2. Do a very rough key on the topmost layer, clamping the white and black areas aggressively
3. Grow the screen (white) outwards
4. Set the top layer as the track matte in the layer underneath

The result is you get a thin green halo around the subject on the layer below (a sort of verdant Ready Brek glow, for UK readers!) that is then much easier to key.