What/how much work experience should I do?

Unfortunately there is no set amount/type of work experience that you can do that will garuntee that you will obtain a place at medical school. From what I understand the medical school are more interested in what you have learned from the experiences you have been through, how you reflect on them and how these have influenced you. I would recomend covering a sort of hospital work experience and a volunteering work experience as they cover a wide variety of skills.