and welcome to the tree!!
It's one of those things that all depends I m afraid. Baby's weight will play a big factor with all nappies and that's one thing no one can really plan for
I used muslins with my youngest 2, but really only for about 2 weeks. I had junior joy ones so not sure on size etc.
I used the origami fold which I found helped catch poo a bit more than the Jo fold as you can adjust more at the leg holes.
Muslins are definitely good on a newborn with regard to bulk compared to an average size terry. They dry so quickly which is perfect when you're going through a million a day/night. I found them to be soaked through within 2 hours though. I think most babies wee lots in the first 6 months as they are taking in only liquid and lots of it, very frequently.
I did try boosting mine which did obviously help and then moved on to prefolds ( as I had them from dd1).
I don't remember there being a problem with nippas although sometimes I think I just tucked the ends in to hold it. I was using close fitting wraps though as I intended to use prefolds afterwards.
Fleece is great and I used from newborn to help catch the poo or slow its progress
and to keep them dry. I ve not heard of using sports tops. I wonder if it would soak wee up too?
Come back with more questions, we need some new Tree babies to look forward to