So from my understanding, you are thinking of taking 5 Alevels and an extra gcse?
It’s completely up to you what you do, it’s important you enjoy what you choose as you will need it especially with the higher work load, however 4 or especially 5 might be quite challenging so I’d think about it thoroughly beforehand if it’s worth it and manageable.
In terms of future options, I was torn between two subjects until pretty close to the Uni deadline, so I wouldn’t stress too hard if you have a rough idea of where you want to end up, but it’s worth thinking about and not leaving last minute.
I’ll keep it blunt, maths or further maths will be hard, any science will be hard, and I’m sure the other subjects I’ve never taken too. Having good teachers whilst it shouldn’t choose your subjects is an important factor to your learning and will make the subject a lot easier.
Most importantly make sure to factor in closer to exams because it does ramp up at Alevel from experience.
I hope that helps!