Which state are you in? The advice I am giving relates to Qld.
I would recommend looking close at what are the pre-requisite subjects for the programs that you are interested in. With medicine there are some unis offering degrees where entry is straight from school and others where you complete an undergraduate degree first. If you are completing an undergraduate degree, it does allow for more time to study subjects which you did not study in high school. Some universities will offer subjects where you don't have to have studied the high school subject. For eg the University of Queensland offers CHEM1090 for students who haven't study chemistry at high school and PHYS1171 for students who haven't studied physics. Their biology subjects don't require any high school biology. However, they cover the content at a faster pace than high school.
Competition for med post grad degrees is very competitive and if you are fortunate to secure a place straight from school, then that is highly recommended.
Medicine is intense and the subjects with the best preparation for medicine are Methods, Chemistry, Physics and Biology. Studying those subjects would make it easier if you go on to study medicine.
However, not all of those subjects may be required for entry to the degree you seek. Doing an undergraduate degree prior to medicine can have its advantages particularly if the degree is in a related field like Bachelor of Biomedical Science or Bachelor of Science. Those programs are less intense but give you a very good grounding and preparation for postgrad med where the content will be covered more quickly. Also, having an undergrad degree under your belt can equip you better with studying the medicine degree.
I studied law and economics at Uni although I only studied economics in first year before choosing to study a straight law degree. Studying law at high school can be helpful for a law degree as it will usually cover an introduction to law, criminal law, contract and torts, constitutional law and human rights law and you will start to learn how to interpret legislation and read and analyse caselaw. Most schools will also offer a moot (mini trial) which is fun. If you study law at uni, they will teach you this information from scratch. However, studying it at high school will give you a head start. It can also give you a taste of what studying law is like. However, there are many more law subjects that you would get to study as part of a law degree.
Similarly, I am not aware of any degrees where economics at high school is a pre-requisite for studying economics at Uni but it would certainly be helpful.
I think the best piece of advice would be to select subjects that you enjoy and are interested in. You will be likely to do better and that can be reflected in your ATAR.
Based on the information you have provided and given you are not sure at this stage whether you want to pursue law/economics or medicine, I would try and keep your options open. I would recommend your 4 definite subjects Methods, English, Chemistry and Economics and then I would recommend Legal and then depending on your preference either Physics or Biology (which would give you a stronger preparation for med). Start with 6 subjects and see how you go and what subjects you enjoy. Check with your school as to when in year 11 do your results start to count for ATAR. In Qld, it is not until term 4 of Year 11 so it does give you the opportunity to see how you go and what you like.
Leading up to that time, consider carefully whether you should continue with 6 subjects or drop to 5 subjects to allow you more time to work on your other subjects. Seek advice from your teachers as well to assist you in making that decision. If you are able to, go to university open days to find out more information about the programs you are interested in.
Ultimately, if you end up studying an undergraduate degree prior to medicine and you are still interested in law, you could study a dual degree Bachelor Science (major in biomedical science) and law or Bachelor of Biomedical Science /Law or Bach Science or Bach Biomedical Science/Economics.
Good luck with your selection and your studies.
