AutoDesk Smoke :: Way To Easily Select A Bunch Of Geoms And Change Their Transparency

I have a Batch with 3 Action nodes inside. Each of these has multiple Geoms tucked away in groups.I only want to see some of the Geoms about half way through the clip.It's raised a few questions:

1) I can only think of animating their transparencies to make them appear at a certain point, is there some other way? Like if it was footage you could use the Timing in Batch.

2)I couldn't find a way to easily select a bunch of Geoms and change their transparency together, I could only do it by using Duplicate mode. But that takes all the parameters from the parent, what if you just wanted to alter one thing?

I could use an expression, but would I have to do that one at a time on all the Geoms?

3) What does the Parenting mode do exactly? can't you just parent thing while in Move mode? What does it add?

4) So I used Duplicate to link the Geoms to one in particular, it doesn't seem to have affected anything I didn't want it to (fingers crossed) and then used an expression on that to link it to a control axis for ease. Does that sound the easiest way?

5) And finally, I was just thinking it would be nice if I linked the transparencies to a control axis of some kind in the Batch, to affect all of the Actions. I half expected to find a 'Control Node' in the box Is there a particular node that would work well as a control axis?