1) If you add points at a later time the spline will maintain it's original shape for the previous keyframes with the new point added. This is good, since other apps have problems where adding points ruins the previous keyframes.
2) Yes. In the rotospline plaette open the wing menu to display the rotospline keyframe editor. At each keyframe is a black circle which is the key (for moving keyframe in time), and below that is a small checkbox. If you uncheck this it will turn off the spline at this frame. So if you want a spline to appear at frame 10 and disappear at frame 20, set you keyframes between 10 and 20, then go to frame 9 and move the spline anywhere to set a keyframe then uncheck the checkbox. This will cause the spline to be off from frame 0 to 9, then turn on at frame 10. Then set a keyframe by moving the spline at frame 21, and uncheck the checkbox below the keyframe. Then the spline will be off from frames 21 and up... sometimes it is faster to just drag the spline off the canvas on the frames you do not need it...
3) Yes. In the player palette, turn on the fourth button on the right on the second row. If you roll over it the tool tip says, "Match Comp to Clip".
4) It depends on the shot. If I shoot on film, I always remove pulldown before rotoing since I then have to deal with less frames and I don't have to deal with flicker frames. If I'm rotoing video, I try to avoid de-interlacing unless it is fast motion with serious flicker frames. If it is a pretty static image, I do not de-interlace since I then only roto half as many frames. The jittering sounds like you de-interlaced your clip with the wrong field order. As for inside or outside, generally if I want to cut something out to go into another plate, I draw the splines just inside of the shape. I usually leave the rotospline feathering off and make hard edges, then feather the matte with the Composite Wizard Matte Feather plug-ins in After Effects (these come with Commotion Pro). If I have fast motion I'll turn on Motion Blur on the rotosplines. Sometimes it is better to go a little outside of the shape if you are doing something like turning the element black and white, like Pleasantville. In this example, you'r better off having the BG subtly grayscale than having any color in your foreground element.
5) (Shameless plug)... my Commotion Complete DVD's will cover everything you ever wanted to know... available from commotionpro.com.
7) The plug-ins in Commotion Pro only work in CommotionPro, similar to how the AE plug-ins that come with AE only work in AE. You need to buy the stand-alone plug-ins for use in AE or other tools. The Combustion keyer is the same as the Discreet keyer found in the Discreet advanced systems like flint, flame, and smoke. It is pretty good, but nowhere as good as Primatte or Ultimatte. We always end up using Primatte in our flint. flame and inferno have an advanced discreet keyer called Modular Keyer, which is exceptional, but you gotta pay to play ($300k+).
8) Yes. My training is really about the concepts more than the button pushing. All of the techniques can be applied to any compositing/roto tool, from Photoshop to After Effects to flame. For example, the advanced matte creation lesson covers channel extractions, garbage masking, articulate rotosplining, matte painting, and other techniques which can just as easilly have been an AE lesson (except Commotion is better for this type of work).
9) Use
http://www.commotionpro.com, and now pinnaclesys.com for Commotion.