LDi.... I scouted around online after reading your post, and..... it's pretty universal - litter boxes = # cats + 1. Actually, 1.5 x # cats, rounded up. Yes, cats that get along really well can do with fewer but they are not pack animals like dogs - they prefer their privacy. With two cats, I have one box in a bathroom upstairs, one tucked in a corner of the foyer and the third in the basement. They both tend to shun the middle one, but... it's there if needed. And yes, I scoop daily. Otherwise, the dogs do.
(I admit it - beagles are gross!)