Why not just internally transfer to science at Monash? Seems like it would be a lot easier for you. Don't buy the myth that there are huge differences between the various universities etc (even includes say monash vs la trobe etc).
(1.) Speaking from the Monash course, both hard and easy. I've never experienced a small course but id imagine everyone knows everyone and there might only be one or two labs, so, once you make friends, you'll see them all the time. Fundamentally though, you are still having contact with people and you can make these people your friends if you work at it, it's honestly not all that dire. Indeed, having so many people to choose from can be an upside because if you dont like someone, you can just move along. Due to the sheer numbers, there are bound to be people who share your interests, whatever they are. Labs i find are great for making friends as well. If you're sitting on a bench for 3 hours while your experiment boils away, you actually have a fair bit of time just to talk freely.
Clubs are much easier and more direct for meeting people however, thats half of the reason they exist and you all already instantly share some interests due to the nature of the club.
(2.) As hobbitle says, of course it is possible. However, it obviously requires a lot of work. Doing first year bio would be easier having done VCE bio but it won't be hard if you haven't, just do all your work and readings and you should be fine.
(3.) N/A
(4.) You need to discern if you actually like neuroscience or the idea of (studying) neuroscience. A lot of people think neuro is cool and interesting but that doesn't necessarily mean they want to (or should) study it. I'll give you an example, i thought i wanted to study history, turns out i just like the idea of studying history. I liked doing casual reading for it but once i had to do a whole series of structured lectures on it (including things i didnt care about) and a whole bunch of assignments on it, i realised it was more the idea of history i liked.
It can become very complex, i assume they just give you a skimmed and abbreviated version for psych. Imagine taking every little thing they taught and exploding each of those things into their own, individual 50 minute lecture on the topic. Chemistry is not really that important at all, especially regular chemistry. Even biochemistry is mostly of dubious help. Biology is absolutely vital with neuro being a branch of biology more or less. If you aren't familiar with biological conceps you will struggle and lack a deeper understanding. So, you will need to be relatively strong at biology to succeed.
I cant comment on UoM quality, its bound to be pretty good anywhere. As for interest, i find it insanely interesting but thats a personal thing. Job opportunities aren't much great or lesser than any other science major, i wouldn't let this hold you back. It will be difficult to get a neuro related job with just a bachelor of science though, maybe some kind of lab technician or medical technician i suppose but those aren't the easiest to get. Ideally, to work in neuro you will get your PhD and become a researcher/lecturer.