I am mostly surprised that it took Van Gaal a week to find a system where everyone looks like they actually have a purpose. Moyes didn't manage that in a year.
I would be surprised if we stick to 3-4-1-2 for whole season. I think Van Gaal is just trying out the tactics to see which fits better. He has the luxury to sign players to make his favorite 4-3-3 work.
with this formation we have to sign at least 2 very good CBs, with 4-3-3 formation we have to sign at least 1 very good CM.