i do legal studies, and it's genuinely one of my favourite subjects. i don't plan on doing law in the future, and even if you do want to do law, those degrees tend to blitz through most of the legal studies course content in the first term, so it's not strictly necessary. however, if you're interested in the way the law works, it's going to be a great subject for you because of just how in-depth it can get. however, a lot of the enjoyment does come from how good the teacher is; if they go through content with background knowledge and give you constant feedback, that's great, but for some of my friends' whose year 11 teacher wasn't as experienced, they had to self-study a lot more and found that their feedback wasn't as good.
in terms of international studies/poli sci like you mentioned, it'll be relatively relevant (more so in year 12), providing one of the electives your school does is either world order or global environmental protection - you'll want to ask your teacher about that one.
not too sure about the exact differences between legal and sac, but i can generally say that in legal essays, you need to be quite good at summarising and picking up the right information. sac also has a major work and there's a lot more personal research/surveys involved, so it's up to you whether you'd be cool with that (legal has no major work/personal research, although some assessments could be hand-in research essays).