damien, you answered correctly for both questions.

To make an alternate "Buss" for sending stems to a single fader, you right click on the arrange window or use the taskbar up top and "Add Group Channel"

name it something familiar, then open your mixer "F3" and expand it to full view by hitting the little "+" button in the top left corner. This will display your ins and outs, for the output, click the dropdown and select your group channel, it's just that easy.

For the automation from a controller on VST Instrument paramaters, open the instrument itself and hit the "R" and the "W" (not on the midi track, this won't do anything but automate velocity, aftertouch, track volume and pan, this has to be done on the instrument or plug-in view page) Next, activate the little red record dot on your midi track so the controller knows which midi track is being controlled, then press Play on the sequencer and twist the knobs during playback.

When you're done, disable the "W" and you should be able to see your knobs moving for you. Then you can open up the controller lane on the Instrument track in your arrange window to see the curves, then you can edit to taste.