Sign Love.
Stretch Wallace.
Look to sign Robin Lopez or Omer Asik. Maybe look into acquiring Roy Hibbert.
Trade for or sign a competent wing. Sullinger and / or Olynyk would be available in any trade.
I think the plan would be to get better by adding Love and a decent center, maybe a decent wing (e.g. W. Chandler), and then as the cap increases and the Brooklyn picks come rolling in over the next couple of years, you have the ability to take the team up to the next level (i.e. top contender) by adding another star to put next to Love.
I don't usually agree with Pho, but he's right on this one. If Love somehow comes to Boston, certain dominoes fall into line.
Wallace is stretched or traded away for a couple of 2nds next year to clear cap space.
Sully becomes expendable and is used as a trade chip as needed for any of the points below. Bradley is also on the block as needed, though Ainge wouldn't actively be looking to trade him.
Ainge will make a huge run at Boogie using everything but Smart. If he can't get him, he'll find a decent center fill in via Free Agency. If he still can't get one, he's moving up to get WCS in the draft.
Ainge would then look to shore up the SF spot. If Ainge doesn't get Boogie Cousins, I would not be surprised to see Kris Middleton brought in as he may be a good pairing with Love. It would push the cap, but it could be done.
But there would be a lot of movement very quickly and Ainge has the pieces to make things happen.