If they can S&T Baby for Landry, they should do it quickly. The Celtics would still have the MLE and the LLE, plus the Marquis TPE to improve their bench, and for reasonable prize (3-4 mil a year), Landry is a great addition. He's an upgrade over BBD in almost every area, except charges taken and defense in the post. But the Celtics still will need Kwame or another 7 footer for their bench, so post defense will be improved in another way.
Ideally, JO and KG start, Kwame (or better, if possible) and Landry would be primary backups, and JaJuan and Green would be third options. That would be a really good interior rotation, if they're all healthy. Add Troy Murphy in a Scalabrine role (but for vet min money), and Semih as insurance for JO, and the Celtics are set in big men department.
Kwame could be had for part of the MLE, I don't think he'd play for the LLE, and there's a real need for him. So they would have the rest of the MLE (if there is one), the LLE and maybe the TPE to get another wing player. T-Mac for the LLE would be great, and resigning Delonte (non-bird rights increase?) would round up the team.
JO/Kwame/Semih/JaJuan
KG/Landry/Jajuan/Green
Captain/Green/T-Mac
Ray/T-Mac/Moore/West
Rondo/West/Bradley
That's 14 players, with health insurance for JO, some money to fill the open roster spot... Of course, it would be great acquiring JR Smith or Jamal Crawford for the MLE, but the priority is a Big Center who can defend in the post.
If Danny can S&T Baby for Landry, the rest of the pieces will be easier to get. Please, NO, S&T Landry to the Celtics, you know Baby is from Baton Rouge and he'll be a local favorite

Too good to be real, all in all...