Huge props to John of Red's Army who does a phenomenal job of breaking down the financial impacts and potential next moves the Celtics could make. Please go read the whole thing but I'll give a brief overview for commenting purposes.
Essentially, Garnett signing for about $10M (with escalators) is a great first step. The next step is signing our own key free agents. That means Jeff Green and Brandon Bass. Then, after signing our 2 first round draft picks, we be over the salary cap but still under the luxury tax line of $70M.
The great thing about that is that we would be able to use both the Mid Level Exception and the Bi Annual Exception to sign other free agents. Details here.
If the Celtics, after re-signing, sign-and-trades, and renouncing, have a payroll of $67 million dollars, they CANNOT use the entire non-taxpayer mid-level because the resulting $5 million will bring them above the luxury tax. The Celtics would then use the TAXPAYER mid-level, which would give the Celtics slightly more than $3 million to give to a player, or split among multiple players, for contracts up to three years.
The downside is that signing Ray Allen would be difficult and expensive down the line, but we've been preparing for that for months now. An interesting twist on this is that it might be better for us that KG signed for $10M than it would have been if he had signed for the league minimum because we wouldn't have been able to spend as much on our own free agents to get over the cap.
So we'd be looking at a starting lineup of Rondo, Bradley, Pierce, Bass, and Garnett with a bench of Jeff Green, free agent X ($5M), free agent Y ($3M), Sullinger, JaJuan Johnson, and E'Tuwan Moore. Not sure, but I'd think Stiemsma fits in there somewhere as well (not to mention Melo, Joseph, and another min level guy). Note: hopefully one of these TBD slots is a backup point guard.
Is that a title contending team? I guess it depends a great deal on the free agents, but it isn't a bad start.
Obviously there are dozens of variations with sign and trade options but this is starting to sound like the most likely outcome. And if it is, that's not a bad thing in my opinion.
Again, go read the article that John wrote. Well done all around.