Thank you all, for the nice words and also for critism!
At what stage it is better to upscale?
That is a difficult question. In past I upscaled as last step. Now as we have AVIR in MLVApp (which I like a lot) I do it in the processing step, before the edit/cut. I'd say for post stabilization and post rotation/cropping upscaling earlier is better, but you'll pay it with more needed disk space.
Any case in which you hand-held the 16-35 and wished you had IS on it?
I really never record video without Glidecam / Gimbal / Tripod / Slider. If I do, the footage is way to shaky to do anything with it

So... maybe an IS helps here.
What gear did you use? Lenses?
I used: EF 16-35mm f/2.8 L II for the wide shots. For the tele shots I used the EF 100mm f/2.0, which were a lot in this video. The 5D3 was mounted on a Weebill S. Audio was recorded with a modded Audiotechnica Pro24.