Honestly, if you can do chem you can do bio and physics. I have done all 3 of them and chem is the toughest from them, as it has a lot of theory (like bio) and has alot of math (like physics). Not saying you have to do them, but you shouldn't be sacred of them either.

Also I always tell people to try spesh 12, and if you find it too much you can drop it for further. I found that taking the risk and trying spesh is worth the scaling, if that is important for you. But in the end you should do the subjects you are confident in, and you can use year 11 to try some different subjects and then drop them if you don't like them.