I do the same subjects at AS
If you enjoy physics it's quite fun to do and doesn't feel like much work. Personally I do M1,M2 and S1 for applied modules in maths&further maths, there's a lot of overlap between mechanics modules and physics so you sort of get taught it twice, but get loads of practice in answering questions. I didn't find myself doing too much work throughout the year, just keeping up with homework and rewriting notes/reading revision guides up until april-may time when I started past papers.
Chemistry is a larger leap from gcse than the others, but it's still just an AS, mostly exam practice and application by the end of it, assuming you're good with remembering ideas/concepts.
FP1 I'd say is quite tough if you had just come from GCSE maths with no experience, I'd definitely have a look at it before you start the year and just get familiar with it as it assumes knowledge from C1&C2 which you won't have finished when you're learning.
If you enjoy the subjects, you could probably only spend a couple of hours each week reading over notes, doing questions from topics you're learning, just to consolidate everything for exam time, we started doing full papers in school around February so be prepared to start doing a lot of exam practice from then.