Mini-Pupillage cover letter advice

Hi! I've just completed my first year and secured a 2:1 and am now looking to apply for mini-pupillages. I have a couple of questions regarding my CV and cover letters.

1) How detailed should the cover letter be?
2) If the chamber has specified to write about any mooting/debating/public speaking experience does acting and performing arts count? (I do not have any mooting experience as of yet - Do I need to provide a reason why?)
3) If the deadline to apply is in August, and I start working part time at a law firm in October but the mini-pupillage starts in September, should I mention that I will be starting a job in the work experience section of my CV?

1) Cover letter should be fairly short if you are also including a CV. Just one or two lines introducing yourself and then a short paragraph explaining why you are interested in a mini-pupillage at the set in question.

2) Is this in the CV itself? I would mention the acting. I wouldn't explain why you don't have any mooting experience.

3) I would include it.