Don't just think about which of biology/ physics your subject combination matches the most - admissions tutors will be looking for actual passion for your subject not just the perfect A levels. I would say that your subject combination would keep open all physics/ biology courses anyway - Further Maths is only recommended, not required (at least for Cambridge, not sure on Oxford) since they understand that not all schools offer it. That said, it is definitely useful for studying Physics at university level - so even if you are unable to properly study for it and take the exams it would still be worth looking through FP1/2 and M1/2/3 if you can.
FM doesn't have a 100% set syllabus - you get to pick the modules that interest you
There are a few required modules (for example I think FP1 and FP2 for my exam board - OCR MEI) and you have to take 3 modules for an AS (and hence 6 in total for an A2).
For example, for AS I took: FP1, M1, D1 and for A2 I took FP2, M2 and M3. There are a few rules, for example I think modules with higher numbers (e.g. M3) require you to also take the corresponding modules with lower numbers (e.g. M2, M1) although there may be some exceptions and variations between exam boards (I'm sure I spoke to someone at some point who did FP3 but not FP2 or something...) but generally I would definitely advise doing the modules in the 'correct' order and not skipping any, since they kind of follow on from each other.
There are also rules regarding the number of AS and A2 modules you can take - I think basically three of your modules have to be A2 ones. You can take A2 modules as part of your AS - but since they are generally harder it probably isn't advisable.
If you are considering applying for Physics, my further maths module combination is probably a good one - although I would perhaps chose to switch D1 for DE (differential equations) or FP3 since those would help with degree level Maths/ Physics, whereas I don't know what D1 could be useful for (except being super easy and guaranteeing 90%+)...
One thing you could consider is just taking your four A levels for now, and if you realise that you really want to study physics at university you could pick up AS Further Maths during your A2s (which would be quite easy since AS Maths knowledge will help with FM).
Make sure you check before you start learning stuff or buying textbooks which exam board you will be using - for example if you can find a fairly local school which will let you sit the exams there as an external candidate and they do AQA Further Maths, then you're stuck with AQA. If your own school is happy for you to take the exams there then you will be very flexible with exam boards - but I would recommend using the same one as you are using for Maths, since then you can interchange some modules between them (which can help improve your grades). I think this is possible if you use different exam boards, but maybe more complicated...
There are a few online resources for maths - for example a 'further maths support network' for self-teachers (google it). However, I would say that the best resources are the textbooks - since they explain things very clearly and include loads of exercises for you to practice. Also, when you're revising just do ALL the past papers - these are available for free online along with the markschemes, often going back over 10 years. For maths, exam technique really is key - so for revision I just did past papers for a couple of months and managed to get top grades.
Also, you talk about 'majoring' in a subject - in the UK you usually only take a single degree subject, with no 'minors', so the word 'major' isn't really used.
At Oxford, they only offer single subjects - e.g. Physics OR Biology OR Biochemistry etc.
At Cambridge, all science subjects are taught via the Natural Sciences Tripos - in your first year you take four modules (one of which has to be a maths module) which can be across a broad range of sciences. You then gradually specialise, and end up graduating in a single subject. I guess this is a bit more similar to the major-minor system, and would particularly suit you if you don't know whether you want to specialise in Physics or Biology - since you can switch between the two. Also, admissions-wise if you are worried about Further Maths affecting your chances of getting in for Physics but are still undecided between the two subjects, you can apply for the 'Biological' pathway and still have the option to take physics modules and specialise in that later on if you wish.