Celtics get under the tax while getting a center for 4yrs. Along with 2 expiring contract who also can fight for a long term contract for the team.
Mavericks need a ball-handling creator to help the team now, also on an expiring deal if they decide he has out lived his usefulness and isn't capable of playing next to Kyrie. While losing Gaford might hurt at the center position depth, it's very manageable with the current roster.
Nets are honestly the hardest, while giving up 1yr contracts are not a big deal you do want some value for them, but also taking on Kuzma is a big-ish ask for what they are getting back. I think its pretty fair but the Nets are definitely the most subject to negotiation. Nothing about their situation makes me think a deal couldn't be met. Kuzma probably stays till the end of the season and gets bought out or gets bought out this season.
Bucks I think get the best possible outcome from getting rid of Kuzma. A long term wing who can shoot on a cheap contract for a starter if he starts to play at that level but is a nice contract for a bench player at his caliber if he doesn't. They also get Klay who can shoot great and will probably look good again next to Giannis.
I more or less like what each team looks like after the trade and this trade could happen today giving every team time to integrate the players before a playoff run if available.