A:Answer 1. The Mark II has better auto focus, vertical recording, and clean hdmi output (doesn't show the settings that you would see on the back screen), along with slightly better battery life.
2. No. Canon has a hard limit of 29.59 for all their cameras (the new R3 is the only camera so far that has the limit removed). If you want to record longer than 29.59 with the m50, you'll have to use an external recorder.
3. Is not possible to take pictures while recording. About the only way to do that is to take the video and pull out a frame of it with video editing software.