What is TSR's obsession with leddit.
It's a shame you don't want to do FP2, where you actually do group theory and number theory (mod arithmetic), fermat's little <3. I'm actually looking forward to it. Nice way to end A Level Further maths - actually doing fun stuff. I'm just not 100% sure if my school offer it (they really should).
I was scrolling through what's in cambridge course and found
the lecture notes for IA groups. The first chapter is surprisingly quite accessible. As I got towards the end of the first chapter, I just got confused and left it there, Past the first chapter, I don't know what the **** is going on . But I like the way it sets out everything and proves results immediately and is quite concise and dense. If you want to get a grip on group theory (and non-applied modular arithmetic), I would recommend the first 80% of the first chapter on that link. You've given a lot of resources, so I feel as if I have to give one to you.
The prospect of academia never really appealed to me. But maybe that'll change.
Good luck with your hopefully somewhat remarkable ventures.