Yes, you are allowed to do that. I have a friend at Sydney Uni who is doing a similar degree and he's majoring in Philosophy and Ancient History.

Doing a double major would extend your time at Uni, but I'm unsure by how much by. It could only be one semester, it could be an extra year (meaning 4 years max at Uni since a BA is a 3 year degree).

Minors you'll be fine with. In my degree a minor is an optional thing and you can fill it up with random electives if you want (do business, then anthropology, then philosophy etc) and my degree is almost the same as a BA. As long as you meet your degree's requirements then you should be okay.

A BA at Macquarie requires you have a qualifying major (you can have more than one) and the completion of a People/Planet Unit (which are just random units chosen out of nowhere for variety. They range from drug studies to statistics to physics etc).

I hope this helps. Send me an email and I'll be happy to clarify anything.

You likely can, but whether this is best is another question. You want to focus and really explore in graduate school. Don't spread yourself too thin as an undergrad.