Excellent advice provided above.
I cannot comment on the particular schools, but I would suggest that if you are 100% focussed on medicine then I would give that application process some thought.
It is very time consuming. Not just in year 13 with UCAT, early applications, interview prep and A levels. In year 12, to have a rounded application you will no doubt be looking at perhaps volunteering, gaining work experience in a customer service people facing job, gaining work experience in a clinical setting, getting grades for predicted A levels up, and any other extra or super curricular activities that you wish to do to aid that application. You will also want to have some free time if you are doing all that !
Think carefully about your commute time and timings. Bus train times etc. do you have the capacity to do all that as well as 4 A levels?
although it is of course possible that application processes might change in two years 4 A levels are rarely required, and 3 is the standard. An EPQ is actually of more help than a 4th A level as some unis give grade flexibility if you have an A in an EPQ.
The most important thing is to get 3 As minimum at A level and a pass in the practical. So Bio and Chem give you the most choice of med schools and the third subject not so much. Psychology is a popular choice as it often is counted as a third science bUt is a descriptive and essay based subject to give you skills that way.
Lastly, learn a bit about the schools and your home situation. Are the schools supportive and where can you do your best work. Are they used to early applicants? Doesn’t have to be med, but need to be geared up to support you.
Are they getting good results? Are they selective or independent? Are they schools which are seen as struggling or developing? T looking further ahead to actual applications your application may be treated differently if you are in a state school or a selective school. But you may do better at a selective school if greater support.
Lots of stuff to think about, the time thing is the biggie for me as I hate a bus journey! Where do you want to go? Where will you be happy?