Small Fits a 29-34" (73.7 - 86.4 cm) Waist
Medium Fits a 34-39" (86.4 - 99.1 cm) Waist
Large Fits a 39-44" (99.1 - 111.8 cm) Waist
Yes, it will work with all other pouches that has a belt loop, which most do.
Yes! That's the whole point of this belt, just remove the Lens Strap (or don't) and you're all set!