I can't answer questions 2 and 3 but, like bbelius said in 1, it all depends on your workflow.
Personally, I like inserting certain Vienna Suite plugs like, Power Pan EQ and Converbs, into Vienna Ensemble for several reasons, one being, I already have my templates built with those plugs set although I might adjust them depending on my needs. Also, I believe if you insert the plugs in the VE instance it will reduce the strain on your CPU then if you inserted them to individual tracks within the DAW.
However, other plugs like Compressor, and Limiter, I'll insert on the audio track after bouncing in the DAW.
Then you have the multiband limiter, master EQ, Hybrid Reverb, and Analyzer which should be inserted on a Bus like the master for mastering.
I think for once I actually agree with Mr. Zimmer on this one.
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Have a Happy New Year