I have to admit this took me longer than it should have to figure out. I was in debate between installing 5 or 6 taps. The collective advice, which was unanimous amongst drinking and brewing buddies was to go with 6. Go figure... Not to mention the non-drinking members of the family like the idea of homemade soda's.
I went with 4" center to center spacing and it looks perfect in person. Holes were pre-drilled with a pilot hole and then I moved to a uni/step bit to finish out at 7/8". Any deviation in horizontal alignment was minimal and the shanks needed very little persuasion to get in. I contemplated a backer on the inside between the shank nut and wall but skipped this option after realizing the aluminum interior was sturdy enough.
As far as the taps go these are Perlick 630's. I love them but have nothing to compare them against.