Haste isn't going affect whether your GCD locked on a pally or not. Outside of taking Holy Prism or getting a lot of Grand Crusader Procs the Pally rotation will always have empty GCDs. At least until you get CS down to a 2s CD, or about 250% haste. There's really no point being Prot on the timeless Isle Pallies scale really well with vengeance which means they hit like wet noodles at low vengeance. FOr the Timeless isle go ret or go Holy, both will out DPS you.
2) SP is eqaul to 50% vengenace if i recall correctly, which gives more will depend on how much master or vengeance you currently have at any given point.
3) any fight where you EHP is challenged.
4) Thecks stop/go traffic light one works fine.