Oratory I agree. Comments like this Doing history won’t help. are plain daft.
All education helps. Wider knowledge is a good thing. Even doctors have to be able to write.
In terms of three or four, a lot depends on the student and the school. No medical school will ask for four, but you need to be able to juggle quite a heavy workload when you get to University sso the experience can help. Quite a lot of pupils, often those from Grammars and private schools will have done four.
DD, who has just started her second year, took five. She has used them all. She was lucky in that she was a natural mathematician and scientist so it was not too taxing and did not prevent her doing plenty of other things. However some of her peers claim to have had to work very hard into order to achieve the right grades in three, so there is not an obvious answer.
In terms of subjects DD says chemistry and maths have proved the most useful. Not having maths means there is a bit of ground to make up. Relatively few have physics, but having it and the ability to pick up concepts quickly, has come in handy. DD is thinking of intercalating in medical engineering, so it may yet prove its worth.
DD did not take a humanity. She has had to do a couple of longer pieces of written work where the structure, evidence and argument skills learned in history would have helped. But again you can only do what you have time for.
BMAT tests on physics as well as other science, which is worth considering if she is interested in BMAT schools.
Bubbles claims that volunteering is more important. Though I will defer to her greater experience, I am not so sure. DD did quite a lot, but she enjoyed it, and it has helped with a course that is quite hands on from the start. Others seem to be fine with very little.