If you don't want to be frustrated while using a microscope, you're probably going to need something a little more advanced than the AM162C. To use a microscope effectively at 400x, you need one with an X-Y stage movement. The slide clips you'll find on that scope and other inexpensive scopes work okay at low magnification but even at 100x they become frustrating.

You're probably going to be over the 300 AUD mark. Take a look at the Swift SW350B. It has a binocular head, which you will come to appreciate a lot. It also makes things easier to use with your phone. You'll want to get an inexpensive phone adapter. I have this one and it works well. https://www.amazon.com/gp/product/B08YWV7V8C/

If you plan to do a lot of photos or videos, you might want to bump up to the Swift SW350T, which has a trinocular head so you can use the binocular part for your eyes and the third port for the phone/camera. That's probably going to cost an extra 50 AUD and you'll be bumping up against your 500 AUD limit.

The other things that these scopes have (that you don't find on the inexpensive beginner scopes) is the X-Y mechanical stage movement and an actual condenser that you can adjust. Having the "real" condenser also makes it relatively easy to add filters for things like darkfield and oblique microscopy.

It's relatively easy to get and install better objectives if you ever want to go that route. Changing the head from monocular to binocular or trinocular is much harder to do. With either of the scopes I mentioned, you probably will never need to worry about getting new/better objectives, though.