If that is all you are using, you may need quite a few.

You may get a chucky baby, so you will need enough to keep going when washing some.

Probably want to get a couple of fleece ones as well. DD was born in late november here in perth - it was high 30s-45 degrees for the first weeks of her life, I had 6 muslin, 3 double layer cotton and 3 fleece wraps. A couple were quite large - I still use them now and she is almost 2.
Charlotte wasnt chucky though

Good luck with your upcoming birth!!