You may be able to take external modules. According to college regs you can take 30-credits of external modules in the second and third year. However, you have to arrange these with the external departments. This depends on whether they will allow you and whether they have space.

The personal statement matters. I don't think it matters as much as applicants think it does. The people that read these will be reading a lot of them. So, keep that in mind. Try to be concise. Explain why you are applying for the subject. What interests you in the subject and why. Personalise it as much as possible. Maybe add in something unique to you. A book you've read or a scholar/approach you are interested in. Explain how your academic career prepares you for the programme of study. Then maybe discuss how the programme of study will help with your career goals and aspirations moving forward. I would try not to use too much academic jargon.

There were 1500-ish applications for PPE for 2024/5 academic year. We've made 600(ish) offers. Target enrollment is 113. We've got 200(ish) firmed applicants so far (not all of these will enroll). I would imagine we are going over target in the 24/5 academic year to make up for a predicted shortfall in postrgraduate taught applications (across the university and sector). Generally, we make our target and often with PPE go slightly over.