1. Can multiple clips be used and compiled into one video?
2. Can a mission be retried?
3. Can skills be changed between missions? (Answered in another thread but just want to make sure.)
4. Can characters be changed between missions?

If you mean ironman,it has to be one run.I believe you cannot switch chars and you can't cut it at all.

1. No thats stupid
2.Yes
3.Yes
4.Yes

1. Preferably not
2. Yes of course
3 & 4. depends if you allow yourself to or not, there's no fixed rule about this so choose it yourself (and we might add variables if you want)