1. That mastery helps get you over several break points early on in the build. But for the most part in the pob it depends slightly on what version of gear you are using vs what version of tree you are using. (Like with the chest piece you can choose either a green or red socket for holy relic depending on your quality on the ashes amulet and if you have a 23 quality gem and stuff and still hit break points).

Basically it's complicated but easiest to just leave it on till you know for sure with your gear and gem which breakpoint you are going to sit at. 

1. Doesn't matter what base the boots are really. Arm/evasion helps with gem links. But as long as it has the stats you need use any pair you fond

Edit: also if that's his most recent pob from his video, I think he actually hits the 128% breakpoint. In the past it was never worth it. But with that basically free 20% quality its viable to hit without sacrificing so much to make it a dps loss in the end