Those guys are right, Commotion was strong but Silhouette roto and paint are even better, and cheaper! Check em out at silhouettefx.com. As to your question about workflow, Do anything you can to the image before you start articulated roto. (i.e. garbage matting, keying) A good roto program will also have a motion tracker so you can apply tracking data to your paint strokes, splines or control points on your spline shapes. That can greatly speed up the task!
If Commotion’s web site still exists, there were some great paint and roto tutorials on there you should check out. The principals taught there can be applied to any software package (thank you Scott Squires). Hope this helps!