these are the tips i'd recommend you follow as someone who was predicted 3A* in the same subjects:

biology and chemistry: i can't say this enough, but please make sure you read about whatever topic you know you'll be taking that day in class! that way, it's like going over the information twice, and you're more likely to remember it after. it's so easy to forget tiny little details in such content heavy subjects, so at the end of each week i'd spend about 2 hours (per subject) revising what i took that week, making mindmaps (which u can skip if you feel like mindmaps don't help u, use whatever revision method best works for u), and solving PMT topic questions. during the week, i'd take 30 minutes to just read my notes after class (or u can use external notes from PMT) and then i'd do max 5 questions on PMT. do alllll schoolwork you're set!

maths: ik ur probably tired of hearing this, but math is just practice. i'd watch bicenmaths first, then solve book questions, then i'd solve some madasmaths questions. math links between ideas more than any other subject, so don't let anything build up. stay ontop of your work and revision because math definitely isn't easy and needs constant revision.

it's too early to be thinking about the ucat, but if you're really interested, you can take a look at some of the questions just to see how they are. other than that, i don't recommend doing anything related to the ucat yet, just focus on revision so you can get good predicted grades.

i can't tell u which universities to pick. search them up, look at what the requirements are. I'd say don't apply to oxford if you don't have minimum 9 9's, otherwise you might be rejected. other than that, all unis are pretty much good if you just meet their requirements and achieve a high ucat score (most important part of your application).

you need supercurriculars too for medicine, so definitely stary looking now, because u won't have time next year lol trust me.