I hate to put the cart before the horse but if the Celtics pull off the Gordon Hayward signing and Paul George trade in the next week or so, Danny Ainge's focus will be on filling out his roster.
For the sake of this post, let's assume that the Celtics part ways with Avery Bradley, Jae Crowder, and Tyler Zeller in order to get George. Bradley may be moved in a separate deal to clear cap space and acquire a draft pick that could be used in the deal for George. Indiana is likely to demand several first round draft picks and it's possible that the Celtics will include the Lakers/Kings pick that is owed to them by the 76ers as well as the 2019 picks that are owed to them by both the Grizzlies and Clippers.
With Bradley, Crowder, and Zeller out - and for cap purposes, this also means good-bye to Kelly Olynyk, Jonas Jerebko, Amir Johnson, Jordan Mickey, and Demetrius Jackson - the Celtics will have a thin roster. That is the reality of loading up with stars in the chase for a championship.
Under the assumption that the Celtics are getting Hayward and George while bidding farewell to the previously mentioned players, their roster would be Hayward, George, Isaiah Thomas, Al Horford, Marcus Smart, Terry Rozier, Jaylen Brown, and Jayson Tatum. 2016 first round picks Ante Zizic and Guerschon Yabusele could also be added but there are conflicting reports on whether the Celtics can afford both this season due to the salary cap.
The starting five would likely be Thomas, Smart, Hayward, George, and Horford although Jaylen Brown could be substituted for Smart. The bench would then be Brown (or Smart), Rozier, Tatum, and Zizic. There is some serious young talent on that bench but for a team with title aspirations, some veteran depth would be required.
Being over the salary cap but not paying the luxury tax would allow the Celtics to spend the Mid-Level Exception (approximately $8.4-million) and the Bi-Annual Exception (approximately $3.3-million). These two salaries would make Celtics ownership pay a premium price for their roster but they could also end up being the difference from just getting back to the Conference Finals and winning the 18th Banner for the franchise. For evidence to that point, James Posey and Eddie House were signed in the summer of 2007 to fill out the Celtics bench and they both made major contributions to the 2008 title team.
Adding a veteran big man would probably be Ainge's first order of business. One intriguing name is Marreese Speights. At 6-10 he can play both forward and center and with a career mark of 35% from 3-point land, he would seemingly be a great fit off the bench in Brad Stevens' system. Speights also has championship experience as he was a valuable role player for the 2014 Warriors. Another player to keep an eye on would be Aron Baynes. Baynes isn't a 3-point threat but did shoot 51% from the field last season and is a better rebounder than Speights.
A cheap veteran guard option for the Bi-Annual Exception would be Anthony Morrow. A nine-year veteran of seven teams, Morrow would add experience to the bench and also his 42% career mark as a 3-point shooter.
Other cheap options to fill out the roster would be Gerald Green returning on a veteran minimum deal, 2016 second round pick Abdel Nader, and 2017 second round picks Semi Ojeleye, Jabari Bird, and Kadeem Allen.