Less than Mancini's side (29) would be my bet.
It's hard to guess just because there's such a small sample size, I feel we could completely shut out the small sides and concede about 20 all season, but we could also leak a few as fixtures get congested and Pep throws people like Mangala or Tosin on to ease the pressure on Stones and Nico when games are already won.
I think we'll be top 2 in the league overall though.
On a slightly related note, the record goal difference is 71, and I think we will beat that too.