If you really think you won't be able to achieve a high mark in chemistry don't pick it, because at the end of the day you won't be interested and it'll drag you down. But the only issue is I really think you need it for medicine. Also economics is just mathematics with finance content, but it...
You are choosing a lot of content base subjects, but if you're organise I think you should be good. Just remember that you'll be able to drop a subject in year 12 if the workload becomes too much in year 11.
You mainly do types of reactions, balancing equations, bonding and also a new task they moved to year 11 titration which is part of separating techniques. So it's all mainly surrounding math but you have to understand the concept and if you do you should be good.
If you want to do medicine I'm pretty sure chemistry is a prerequisite, it is hard but if you focus on it you should be fine. But it's also a math base science if that helps.