Let's break these down, shall we?
Boston (idea #1):
Boston: DMC
Kings: Johnson, Ollynyk, Rozier, Nets 2018 pick, Clippers 2019 pick, and Memphis 2019 pick
So the Celts give up Amir, KO, Rozier, and three first round picks, including a BRK pick.
Pros: Three rotation players for one superstar big. That's a great deal. The three picks are a lot to give up, but there's not much room for picks on this team anymore, is there?
Cons: There are 1.5 years left on Cousins' deal. I wouldn't bet much money on DMC staying in Boston if the team doesn't enjoy immediate success. That's a lot of risk.
Would I do it: Definitely. You get Cousins without giving up more than one BRK pick and you keep all of IT, Smart, AB, Crowder, and Horford. No brainer.
Boston (idea #2):
Boston: DMC and BMac
Kings: Smart or Rozier (Kings choice), Johnson, Rights to Yabusele, Young, Nets 2017 pick, 2018 Boston 1st, 2019 Clippers or Grizzlies 1st (Kings choice)
Two rotation players, two prospects, and three 1sts, including one BRK pick.
More or less the same analysis as above. Could be expensive to keep KO along with everybody else next summer.
Would I do it?
Definitely. IT, AB, Crowder, Horford and one of the BRK picks remain after the deal. No brainer.
Two part Boston-Timerwolves-Kings trade:
Boston: Rubio and Timberwolves 2017 1st
Timberwolves: Rozier, Johnson, Timerwolves get back their 2017 2nd round pick, and Boston 2018 1st
Second part of the proposed deal (now that they've acquired the big guns):
Boston: DMC and "filler"
Kings: Rubio, D. Jackson, Jordan Mickey or James Young, Nets 2017 pick, and Minnesota 2017 pick
This one is excessively complicated. Basically, the Celts give up Rozier, Amir, 2018 1st, Jackson, Mickey/Young, Nets 2017.
Again ... you get Cousins while keeping IT, AB, Smart, Crowder, Horford and one of the BRK picks. I think you gotta do it.
Boston (idea #3):
Boston: DMC and WCS
Kings: Nets 2017 and 2018 pick swaps, Zeller, Johnson, Rozier, Young, and the rights to Zizic
Both Nets picks, Zeller, Amir, Rozier, Young, and Zizic.
That's too much.