When Tamagotchi P1 and P2 first came out, I was in 5th grade and I would care for up to 14 at a time. Yes, 14. And, yes, I was insane. ^_^ I would have them clipped onto all of my belt loops on my shorts throughout school and everywhere I went. I don't know how I did it, but I did. lol
Nowadays, though, I only comfortably raise up to 6 at a time. With work and college and things, I couldn't logically raise many more than that, and expect to be able to care for them properly.
Currently, I am raising 3 V3s(Warusotchi, Megatchi, and Kinakomotchi), a 22 year old Genjitch(a secret character), and a Mothra(Batora).