I like this move for Boston. We weren't going to ever be bad enough for a top lottery pick, so might as well make whatever roster improvements you can, especially at such little cost. This should give the Celtics pretty strong odds of making the playoffs again.
I think Zeller, Johnson, and Lee will form a nice three-man big rotation. They aren't an elite trio, but they are certainly an improvement over what we had last year. I hope this means Sully and Oly are gone, I don't see how either has a role with the team now.
I think I would start Zeller and Johnson, and bring Lee in off the bench as the first big at either position. Jerebko can get the rest of the minutes.