When you speak about who the Celtics will go after in free agency, make sure you take into consideration the style of play the C's are aiming for, and the age of the player. Pau is a good fit, if he we're 8 years younger.
Mozgov is an aircraft carrier that must be planted next to the basket, that's not what DA and Stevens seem to want.
If Cousins we're sane, he would be a great fit, but if he we're sane he wouldn't be available.
The Celtics, like many teams in the NBA like to play small more than 50% of the time. It doesn't make sense to sign a center with a big name, for big dollars, when he may be sitting over half the game. I'd rather them sign a young defensive minded center (John Henson, Ezeli) for reasonable money, and go after additional scoring.