As of now, without any additional major moves, I see the team moving Niang into an exception. That would put the them around $12.5M under the 2nd apron. If they are serious about competing, they could still re-sign Horford and Kornet for around taxpayer MLE money and then sign another player using the taxpayer MLE. Since those roster slots are already accounted for with $2.3M salaries, that would only add between $9-10M, still leaving them slightly below the 2nd apron. So maybe the team would like something like this:
White/Pritchard
Simons/Scheierman
Brown/Hugo/Walsh
Hauser/MLE FA/Craig
Horford/Kornet/Queta
With Tatum, that is 14 roster spots filled, which is what I think they'll go into the season with. They'll also have Shulga, Williams, and either Norris or Peterson on two-ways. Maybe they even convert Peterson and don't resign Craig (or sign a different vet min altogether).
I'm not sure Davison makes the cut, but it looks like our guard rotation is a little light, so maybe the MLE FA or vet min goes to another guard. Either way, I think this is the framework of what we should be looking at this season, which is still a competitive team. And a very competitive team if Tatum comes back. In short, I don't think this is a tanking team.
EDIT: And right after I write this, I see an article from The Athletic/NYT that the Celtics are looking at shedding more salary and are exploring the idea of trading Simons. If that happens, then I guess it doesn't look like we are trying to be all that competitive, especially if the goal is to get under the tax.