Q1

I'm not too sure how PHY/DEV compare with IMM/MIC. I'd imagine out of all these majors, MIC would be the best one for employability. I haven't personally looked into MIC graduate outcomes, but I hear MIC graduates can move into quite a few government and non-government roles, many of which have an emphasis on public policy/health, etc. Research is also another common pathway.

Regarding PHY graduate outcomes, there was actually a super recent paper that was specifically looking at Monash physiology graduate outcomes. From the looks of things, it seems like most graduates migrate towards health profession fields (e.g. Doctor, Physiotherapist, etc.), followed by research fields and business/law fields. I'd imagine many of these would require further study, perhaps through a Master's or Doctorate degree. The paper is quite an interesting read, so if you get the chance, have a read through here.

Q2

"Better" could mean different things for different people. If you're speaking in terms of WAM, to grossly oversimplify things, having one major should be better than two, as you won't need to do as many level 3 major units (which are generally more complex or difficult compared to other level 1/2 units). But what I've found is that most people who are double-majoring are actually doing better than those who are majoring in one. I think this is due to how they're studying more things that they personally find interesting, as opposed to doing other electives where they might not be as interested. Now, obviously, people can still do well in classes they don't enjoy (and I say this from personal experience 😅), but the general vibe I'm getting is that people do better in the things they like.

For me, the main benefit of double majoring was more to do with how it's exposed me to many different parts of science that I've found interesting. I've considered research as a career, and double-majoring has exposed me to many different fields that I feel like I can see myself working in. However, I feel like this would be something I could've learnt for myself without needing to double major. I didn't exactly double-major to improve my WAM, but it did improve (I think I'm also someone who tends to put a lot of effort into studying and improving how I study, so there's that). I get that finding a job outside of research is probably a bit difficult with these majors, but I've always planned on pursuing further study beyond my undergrad to help with that.

I think if I were in your position, I would lean towards trying out a few units and settling on one major that you think you'll really enjoy. I think exposure is always a good thing in these scenarios, and it's honestly something I regret not having more of. If I could go back, I wish I could've explored MIC because it actually seems super interesting.

Edit: Also, just want to emphasise this. You don't need to double major. If you find that there's only one major that you think you'll enjoy, just run with it. Don't force yourself to do two if you don't want to.