A week ago I transplanted mine, which were 3 weeks old and 3-5 inches tall in 1 by 2.5 by 2.5 inch pots, to pots that are 4 inches square and 5 inches deep holding a quart of soil. I placed the soil block from the original pot directly into the bottom of the deeper pot and gently filled in around them. In some cases the first set of true leaves were buried and only a tuft of the second set were visible above the soil. They have all grown considerably in the week since and look great. Go as deep as you can. I'm hoping mine will be able to go out for hardening off in 2-3 weeks.

I'm doing mine tomorrow, but since I have limited space indoors right now I'm just going from 72-cell flat to 50-cell flats and 1 plant per cell instead of 2 (or some cases, like cherries, as many as 6!). Had started seed March 16 but then had a few varieties I started later, and I've still got some emerging (they've been off the heat for weeks, I really thought I wasn't going to get any more).

I'll go to 3-4" pots later in the month, or early May, start hardening off mid-May.