Hii!! I'm currently doing my A-Levels and one of my subjects is Politics (Edexcel, so my answers might not be relevant to the exam board you might do)
1) There's isn't really any choice in what you learn but it's pretty broad too. The only major choice I'd say is for Paper 3 where the options are either US politics or global politics (I'm doing global which is pretty fun because as you learn, you realise how relevant it is to the outside world, e.g. when we were learning about the ICJ, at the same time South Africa filed a case against Israel and so it was fun to see how what we learnt was implemented into real life)
2) I think personally, I enjoy politics, especially in lessons, but that might also be due to having fun and good teachers. Doing exams however is another thing but to be honest, if you stay on top of what's happening in the news and revise, you should do well in the exams so I would say it is enjoyable.
3) I don't do either so cant comment, sorry!
4) Yes, the topics are very broad, annoyingly so. You do learn a good amount for each topic I say, and honestly because it is politics, once you learn it, it kinda sticks since, as I said before, it's all visible in real life. Like, let's say we learn about how laws are passed within parliament, now when I see bills being proposed or passed, all I can think about the process it had to go through in order to be passed
All in all, I think politics is a good a-level if you're willing to take time out of your day to see up to date and whats happening in the world and if you like writing essays, it's all essays!