It really only depends on your own personal comfort level. I know providers who take on 5 one year olds at a time, and prefer all that age.

If your home/daycare is set up in a way that makes for easier access to outside, nap and eating areas, etc. (because one year olds are less mobile than older kids), then you'll find it less work than if you have to navigate a lot of stairs constantly throughout the day with the little ones... but it certainly can be done.

I'd recommend starting them gradually though, so you have time to transition them one at a time and not end up with several screaming babies at once, lol.