There are two ways to do it. not everywhere offers both ways...so one deciding factor might be what is avaliable near you.
first way is being a nurse first = you need to do the 3+ year bachelor of nursing, and then 1 year post grad dip of midi. some courses also require you to work as a nurse for atleast a year before doing the post grad.
the second way is to do a 3 year bachelor of midi - this is fairly new in australia and isn't offered everywhere.

there are pros and cons for both ways, and it would depend on alot of things. I personaly think the nurse first/aswell is best, yes it takes longer, but i think the skills you get as a nurse you will use forever, i am using them in my day to day life as well as my midi. Plus it opens more doors and gives you more options work wise.

good luck!!
YES all of that I agree with doing nursing first as well.

Good luck its a great career