Danny's options, on initial reflection:
Trade #1 to CHI for Butler (18.7mm salary for 17-18, contract through 18-19 with a player option for 19-20)
Trade #1 to IND for George (19.5mm salary for 17-18, with a player option for 18-19)
Trade #1 to PHI for #3 and Saric (2.4mm salary for 17-18, with control through 19-20) (BOS then picks Jackson or Tatum)
Trade players and one or both 2018 first round picks (but not this year's #1) for Butler, George or other players
17-18 guaranteed contracts (61.8mm total):
8.8 Bradley (FA after 17-18)
6.3 Thomas (FA after 17-18)
4.5 Smart (FA after 17-18)
0.7 Jackson (guaranteed portion of contract only)
Cap holds (37.1mm total):
Assumes Zeller & Mickey options are declined and DJax is waived.
Salary cap is 103mm. Luxury tax is 123mm. If the rights to all free agents but Olynyk are immediately renounced on July 1, the Celtics would have 33.5mm of room under the cap with 7 players under contract, less cap holds of approx 7.0mm for the #1 pick (note 17-18 slots have not been announced), 2.25mm for Yabusele, 1.65mm for Zizic and approx 0.8mm to fill out the 12-man roster, based on minimum salary requirements.
That would leave approx. 21.8mm to sign a free agent (Hayward, I presume) or trade for Butler/George. Renouncing Olynyk would get them to 29.5mm, slightly under max room (30.6mm). Actually signing the #1 pick, Yabusele and/or Zizic frees up more room because the cap holds are based on 120% of slot.
Obviously, they could trade one of the 7 players under contract or get Yabusele to agree to stay overseas for another year to free up more room.