First thing - don't pick 4 subjects, esp that combo, the workload will stretch you very thin and it will affect ur results at the end of y13 (keep in mind y13 will be even more worse
For advice on subjects: I've heard that the jump from gcse physics to a-level physics is a lot more than the other sciences, a 9 in physics might not mean you'll do well at physics a-level.
As an a-level biologist, there is a LOT of content you need to know, and you'll have to put a fair amount of work into learning it.
Maths is relatively easy if you do well, further maths may be too difficult for a grade 7 student, as it is a course for very gifted mathematicians and can be very challenging, but if you enjoy maths it is fun! It also has a fairly large workload, after each lesson I have to complete an hrs worth of exam questions and I heard for FM it's even more.
Another thing to mention is that it's best to pick subjects that synergise well together, if you learn the same thing in both maths and physics (or FM and bio as there is a slight crossover in statistics) it's more likely to be remembered.
In summary pick the 3 a-levels you enjoy the most, you need motivation to get through these academically challenging courses especially STEM ones. Hope this helped!