Since the launch of Lollipop on the S5 there have been over 500 different Lollipop official firmwares from Samsung as well as the clone firmwares from Verizon and AT&T. See, S5 Lollipop (Android 5) latest releases
The vast majority of Lollipop firmwares are much better than KitKat whilst the Verizon versions have been an unmitigated disaster, by-and-large.
Depends on which model of Galaxy S5 you have. No problems with rooting all the models and firmwares except the latest Verizon OE1 release. See, Verizon OE1 update prevents rooting/downgrading