Definitely not, uni grades are far more important than your HSC because they will be a huge influence on what sorts of jobs you'll be competitive for, and whether you will be able to pursue postgrad
HD marks means you will have a super easy time getting interviews. I know people who send out hundreds of job applications for a single interview. But with high marks, you get WAY more interview offers.
Sorry, but uni isn't a time to chill out and drop the ball. That said, you will be studying courses you actually enjoy, so it shouldn't be too difficult to work hard.
If you're thinking of studying psychology, then this is one of the most important degrees to get high marks in. Psychology is the most commonn degree, so a ton of people graduate with it. If you want to become a clinical psychologist, you need AT LEAST 70 average mark to get into honours, and then you will need first class honours to be competitive for a masters, which is a pathway into becoming a clinical psychologist. If you don't make it into honours, then you're basically screwed as a) you won't be able to get into clinical psychology b) you've got a super common degree so you're not that employable
You need good marks for research. You will want to get funded for your PhD. This requires a) evidence of research in undergrad b) high marks. This is super competitive.
Tbh for me it feels like I'm working way harder than in the HSC. But, the good thing about uni is that we don't have carry over between semesters, so when you're on holidays, you don't need to be studying.
Not a good idea, I don't even know if that's possible. If you want to combine the two, then pick a project that uses both.
Yeah tbh a double degree is god tier imo, it doubles your empolyability options by only taking an extra year. Highly worth it.