Hi Pete

You asked a lot of questions! I can help with some. 

CAMduct is the only thing you will need outside of the AEC Collection unless you want to do estimating using the same Fabrication database, then you'll want ESTmep.

Once you have your Fabrication database configured how you want, you can use the Items in Revit and use Revit for detailing or just stick to CADmep (AutoCAD based). You can save the project from Revit or CADmep so that it can be opened by CAMduct.

CAMduct will work with Vicon plasma and coil line. I don't have experience with their liner cutter.

Spec's are not hard to do, it is just a different interface. Start with getting your materials right.

I have changed a few customers from Trimble to CAMduct. Their motivation has been integration with Revit and a local person they can get support from.

Good luck!