NTSC is used in North America, and PAL mostly Europe and the Middle East. However, almost all devices play both, so not really an issue. PAL uses 25fps frame rate and NTSC uses 30 fps. PAL, on the other hand, has slightly higher resolution, 720 x 576 for PAL and 720 x 480 for NTSC. I have read that NTSC is more suitable for You Tube. It would be your call as to which you prefer. I would go with NTSC since it is more universal and has a higher frame rate.
As for which is best for video, still cameras versus video cameras, at the consumer level it probably doesn't make much difference. Still cameras tend to have better lenses, more lens options, better zooms, and more editing options than video cameras. Some still cameras shoot in 4k video, that is very high resolution. All of them shoot in full high def 1080. So I wouldn't worry about shooting video with your still camera.
You can't record video directly into iMovie except with the built-in face time camera on your Mac. With the QuicktimePlayer on your Mac you can record New Movies, but I don't think that it is possible to record directly from camera to your Mac. This is not something I have looked into much, so possibly there are apps out there that allow direct recording onto a Mac.
As for Skype, I have never used it, so can't comment on that.
-- Rich