What Containers to use? Please advise

I am going to 5 Blue Mystic plants what size should my final container be (how big should my flower pot be)

Well if you want a good size plant I'd say go with five gallon containers if you have room. You have to weigh available space with desired result. You can easily get away with three and maybe two gallon containers, but you'll have to water more often and it's more likely you'll run into stunting and stuff. With a five gallon pot, you can grow a pretty beastly plant and not worry about these issues. Just get some buckets from a restaurant or something and drill a bunch of drainage holes in em. Works great.