1. If you don't know that, I think you make it as a challenge and do some research on it to find out.
2 and 3, I suggest you read up Part 12 of the EA under Rest Days, Holiday and Section 60I Interpretation. You can find all the answers there.
4. Generally, you may do that but you must specifically mention such consequences the staff likely to face in the last warning letter. However, I still think conducting a DI first will be better.