Cool! I didn't take maths HL myself, but I know it's quite tough; a lot of people in my grade started doing it, but then dropped down to SL or even Studies. Be prepared for a challenge; the exam is made to challenge you, and you really have to apply your knowledge to unfamiliar situations (or so I'm told). Perhaps that scares you, or maybe you enjoy a challenge
Students taking maths HL definitely spent most of their time studying for it, though, so if you're not already very good at maths I wouldn't recommend it since your other subjects could suffer.
I don't know about business and management; it seems like it's just watered down economics (which I took) at this level. Economics isn't too hard really; you just have to understand it, and then graphs begin to make sense as well. I think universities look more highly upon economics than business and management since its a more traditional subject etc etc; I'd recommend you take it.
Are you sure your Swedish is good enough to take it at A1? Could be tough, since that's meant to be your mother tongue. I had one person in a similar situation to you, from Poland, at my school; she managed to arrange with the school to get a Polish teacher and do Polish A1. Don't know if your school could do that, though. (I took English A1 (which corresponds to lit in the new system) and Swedish A2 (A1 lang lit in the new system) myself, but I've been learning those two languages since I was very young).
I think Physics is tougher than Biology if you're not into science; but perhaps you are?
Have you studied Spanish before? If you have, even briefly, ab initio should be cake.
Sorry, I don't know much about your school. It seems alright though; and after all, the program is the same wherever you are. Even if your teachers aren't great, you can always find the syllabus and tons of online resources and study yourself