As someone who did AS Maths alongside three other AS subjects (Psych, Econ and Photography), I would say that it’s possible. However, just a heads up that Maths was the most intense of my subjects and took the most time. We have pretty similar subjects, both psych and maths, you on business and me on econ, but my fourth was photography, which was coursework based and, for me, a lot less stressful. Your fourth will be biology, which I hear is quite a lot to deal with!
In terms of applications, I’d just check with the unis you’re looking to apply to. Those that don’t specify they want A Level Maths will probably be fine with no AS Maths either. If your GCSE grade is 7-9, then I’d say that shows that you’re competent enough.
If you’re looking into doing another AS for UCAS points, an A will get you 20 UCAS points, so make of that what you will.
Good luck 👍