#2 - you would need a new BB for a new drivetrain brand. Praxis is their own set up. Seriously if they are not worn out don't change them. Praxis stuff is pretty good.
#4 - everyone had their own opinion on torque, if you don't have a torque for the setting either buy one or find a source to use one. It not a number you have to be spot on but they give a number for a reason. If your off by less than 5% your fine, but over or under can be a problem maker IMO.