Hi there! I'm a scottish student and took 5 highers last year, so I'll try my best to give advice, although I'm not so familiar with the English school system of things.
So I took 8 National 5 subjects in 2022-2023 and 5 highers 2023-2024. Since we take our subjects in one whole course throughout the year and sit the exam at the end of the year, it definitely requires a lot of time management and figuring out what works best for you.
You can start by making some sort of revision/study timetable. In the beginning, since you don't fully know how you might work best, try blocking some small time slots and spread out your subjects. For example, don't work on one subject for too long as you may find this very boring and tiring. You can block parts of subjects as well: like you said you wanted to go over some older content, you could block that in and then block in the learning of new content.
With past papers I like to spread them out over a longer period of time. Before my own exams I like to block out every past paper I have and do one or half every day leading up to the exam (depending on how long the papers are). They can be a good way to gauge what questions are like and the sort of answers and expectations they have. If possible, you can do these as clumping together each topic and do some past paper questions on each topic separately in chunks (this is up to you).
Most importantly, make sure to leave yourself some free time, otherwise you will feel burnt out and then trying to remain on top of your studies can be even more difficult. Remember to think about the big picture.
I think I've covered everything! Good luck with your studies! Make sure you find what works best for YOU as well, after all, we're all different and different study methods work best for different people 🥰