I really can't help you with the IB portion as I am not in IB, but I can answer your 2nd and 3rd question.
2. Prepping for UKCAT is all about practice. Try to do some questions each day to get the feel of it by using the 600Q book and then use Emedica or AceMedicine to get the feel of the test itself.
3. I'm not quite sure what you mean by that. What you say in your personal statement is really up to you. You can talk about your work experiences, your extra curriculars, and basically why you want to pursue a career in medicine. There is no right or wrong answer, but check the internet and resources around the forum before asking yourself this question. But if I were to give you an advice for any part of the application process, it would be quality over quantity. It's about what you get out of all these experiences, not the quantity of the experiences you've had.
Good luck!