I do think you could do it, given the level your grades are at now. For subjects like Maths, Chemistry, and Physics I would recommend doing a lot of questions. That's probably what everyone says when asked how to revise for Maths especially but it's really effective if done properly, if you find things to be easy then try and find harder questions, or ask your teachers to find you some difficult questions to do. Additionally, for these 3 subjects, which tend to have smaller-sized questions compared to other subjects, I would suggest doing a question then marking it, and then doing the next question and marking it right after. Most people would just do an entire topic paper for revision and mark it at the end. Topic papers have multiple papers that are similar to each other and if you find that you have a recurring mistake at the end, you acknowledge it and move on. But if you do this technique of marking after each question, you will be reminded of that mistake that you made in the previous question and you'll avoid it in the new one. I found this to be really helpful at GCSE and A-Level for Maths and Chemistry especially.
Nearer to your final exams though, I would retract back to doing entire papers and marking them at the end so you have a better idea of how it feels to do full exam papers in preparation for final exams. This tip is for practice on something you aren't that confident at/ when you start out learning something new.
For Biology and Geography, where you will have to memorize large amounts of information, you can use the blurting method and flashcards as others have said. Flashcards weren't something I was keen on so I used to go around explaining topics to family. Annoying for them, beneficial for me. I would suggest trying this out. If you can explain a topic or subject to someone and you think it is clear enough, then you know the content well, if you can't explain it or you stutter because you've forgotten things - then you do not know the topic well enough - that's just how I see it at least, others may disagree. If none of your family wants to listen all the time or aren't paying attention (as this does happen) you can explain it to yourself out loud alone and if you think it is clear enough then you've done well enough to memorize. This was my alternative to flashcards for content-heavy subjects.
I can't give much advice on English because I haven't done it in a while but I think you should really exploit your teachers (for all of your subjects really), that's what they are there for and many teachers would love to help. When you write an essay or an analysis question answer go ask your teacher for feedback on what you did well and how you could improve. You could go to multiple teachers and cross-reference their different opinions and later when you have time you could answer another question that is similar and apply the feedback that you've gotten. This also applies to business which, from memory, also has long answer - essay style questions.
Hopefully, someone else can advise you for Spanish - Language wasn't a strong suit for me.
For the structure of your revision, don't do a month on just one subject. By the end of the year, you will have most likely forgotten what you learnt or revised in the first few months. You should create a timetable as another person has said. Many people think that timetables don't work for them after trying it out for a short while as they can't get used to it. Truth is, you can get used to a timetable - don't you go to school every day with a set timetable for each weekday - there's always a period or two followed by a break then another period or two, lunch and etc. Going to school proves that you can follow a timetable - you just need to have discipline and resolve to follow it even when you don't feel like it.
That said sometimes sessions or periods of revision can feel unproductive when you don't like doing a subject and have to force yourself to get through it so if this happens and you don't get enough done in a study period, include a buffer period in the timetable where you have time to finish off any unfinished tasks. There's also psychological research on forgetting things and this thing called the forgetting curve which you should look at - it's a graph that shows how much time passes for the average person to forget something they have learned - I've read something like - you forget 80% of new information that you learn within 2 days of having learned it unless you go over it again.
Also, don't overwork yourself, getting all grade 9s is difficult and requires a lot of effort but that doesn't mean you should enslave yourself to a desktop all day - every day for the entirety of year 11 to achieve it. I mean some people do have this undying willpower to achieve the highest grades who don't seem to be affected by working intensively for long durations. I felt like that at one point. In the long run - you'll feel exhausted - maybe not even at the end of GCSEs but during the beginning of A-Levels. So do take breaks every day and include them on any timetables you make.
Another small tip I have is to not do other things in the same space as where you revise - if you are going to go on your phone for a break - go to another room. Don't play games on the same pc that you use to revise - don't eat where you revise. Reserve your revision space purely for revision - this will unconsciously help you get in "the zone" when starting to revise faster.
I do think you can get all 9s - as long as you are dedicated and disciplined.
Good luck!