I expect them to pick up the speed and tempo of the Cs offense, getting more first option looks in the offense. I think they will set the tone for the offense, making it a bit more frenetic (not quite at the Warriors level of frenzy, but still).
I'd bet you're right about the tempo going up.
The standard way to measure tempo these days is to count the number of possessions - that's logical, but it doesn't separate offense from defense. (You may remember Doc Rivers saying that he wanted a quick tempo on offense and a slow tempo on defense.)
Having said that, here is where the Celtics have come down the last few years in pace (I included Golden State for kicks):
Boston was 16th in tempo last season. Golden State, incidentally, was 11th. Things change.
In 2018, Golden State was 5th, and Boston was 23rd.
In 2017, with IT and Horford, Boston was 12th and Golden State was 4th.
In 2016, Boston was 3rd, and Golden State was 2nd.
It's worth asking if Irving slows down the tempo by dominating the ball.
Free throws and offensive rebounds slow the tempo, and it looks like (judging from the personnel) that those things will go up. Rozier moved the ball up quickly, as well, so the loss of Terry won't help the tempo.
On the whole I lean toward your point of view, though; I think that the pace will be faster.