I don't get all the worrying over Moses Brown. As said above, the main trade was Kemba for Horford and save a bunch of money. The saved money gives us flexibility to be able to consider a S&T acquisition while still dealing with the hard cap. There was no option for this without the trade.
Moses Brown comes to us in exchange for the #16 pick (I am ignoring the 2nd round picks). This transaction will also save on the cap (about $1M). I am sure there will be a long running "what if" debate about this pick but I think it is pretty clear that a player coming off a fairly nice NBA season is likely to contribute more to the Celtics over the next couple of seasons than a rookie would. No way to know for sure, but this me, this is a reasonable play by the Celtics.
Now as to Moses Brown's ceiling, we know that at age 21, he played 43 games, started 32 and put up 8.6 pts and 8.9 rebs. To me, that says the floor is 9 pts/9 Rebs, some are saying that is the ceiling. Rob Williams, who is 6 inches smaller and 2 years older, has not produced that. Tristan's best season was 12 pts/10 rebs but was around the 9/9 mark most of his career (in generally more minutes).
I believe that Moses Brown is going to be a useful player for us next season. I also believe that Thompson and/or Williams will be traded. More useful than Kornet, GWill, Ojeleye, and possibly even more than RWill and Thompson.