It was 31, and Sterling is also notoriously robust and played 4000 minutes that season. His conversion rate that year was better than the likes of Salah and Mane, and he scored above his xG, so he wasn't missing any more sitters than other top strikers.
In terms of minutes, none of the other attackers have ever got close to that figure under Pep (Kev has, but he's playing further back much of the time). The main rotation happens up front and last season, Phil was our front player with the most minutes and he played the equivalent of 35 full games across all competitions. Haaland has only had one season where he played over 3000 minutes, and even then, was nearly 500 minutes less than that Sterling season.
The Bundesliga is also a lot easier than the PL (which is a lot harder than the CL and international football), so you would expect some drop off in scoring rates.
I'm really excited for him - and think it'll be fascinating to see how he plays, and how City work with him, but I just don't think we'll flog him to death given how many injuries he's picked up already in his career. He's at City as a long term player, and we don't desperately need extra goals in every game we play.