How do I manage the workload of an EPQ alongside other A-levels?

I think the most important skill to develop is time management and scheduling ability. Try to assign specific times each week that are solely dedicated to working on your EPQ. If your timetable has free periods I personally found these to be the best times because it meant I still had access to all the relevant files. Depending on what your EPQ entails, I would say try to work on your EPQ for at least 3 hours a week, although if like me you're doing something with a higher work load such as writing a book (I did this), you might want to consider dedicating slightly more time.