If using a lot of the same paint I would go with 5 gal buckets, don't have to worry about possible shade differences between gal cans. Best to use a paint mixer bit that attaches to a drill and a pour sprout that attaches to the 5 gal bucket, each a couple dollars.
And with paint cans of any size (well, except maybe quarts) ask them to use their paint-mixing machine to mix the paint, especially the 5-gallon size. Even if it's going to sit for a week or three that will make the final mix before you paint much easier, and it may mean you don't have to mix it at all.
Other than that I can't add anything that hasn't already been said.