Easy question!

If the pattern says there’s “2-4” of ease" does that meant that if I pick the 36 measurement that I can expect that it will be 2-4" bigger than that? That’s what I’m hoping for! Thanks!

If 36" is the body chest size measurement, then yes, 2-4" of positive ease would be 38-40" on the finished garment. You can usually confirm this by looking at the number of sts across the chest and the pattern stitch gauge.
Which pattern are you making?

I’m making the Berroco Royston with the recommended yarn, Maya. I have made their patterns before. The only thing I have to fiddle with is that I don’t have a 29" circular (I already did the gauge and it’s perfect!). I have a 24" and a 32". Since it’s in the round, I was going to use the 24". Does it matter much?

Mmm, very light and pretty.
I’d go with the 32" just so the stitches are less crowded but that may be a personal preference. It’s knit on one piece so you’ll have 38-40" on the needles.