Hi, this is unlikely to be the reply you would want, however I am wondering whether you could drop one of these subjects? Are you able to study Russian recreationally and open up some revision time for your other subjects, or let go of the EPQ, knowing you are already showing your breadth by studying languages and maths for example?
I do not doubt all your subjects provide you different skills and advantages in the application process, but it may be hard to maximise your grade potential when you are balancing so much, meaning you may actually forfeit offers.
I really wish you well, and know that my experiences are not at all universal. I am taking my 3 A-Levels this year (also expected high grades like yourself) and tried to make it as simple and efficient as possible, making my goals realistic. This meant me dropping EPQ, and funnily enough, not taking the Russian A-Level (what are the chances!).
Giving yourself free time and lowering the pressure may result in a better performance and likely reduce burn-out.
However, in terms of practical advice for revision, especially maths, drill the mixed exercises for each topic in your textbook and give yourself strict timeframes. Similarly, do practise papers in less time than normally given. I find that with maths, often it's not that your knowledge isn't good, but that knowing what maths knowledge to apply to each question, and fast is what boosts the grade. Also, knowing when to give up and go on to the next question, to return to harder ones at a later point in the exam.
Hope some of that was useful. You're doing really really great, and your ambition and breadth of interest already speak volumes, so I wish you all the best!!