Anyway. Assuming whole building hall with 3 sections has each section launch a sub in 3.5 years in the beginning and launch a sub in 2 years after years of experience: in the first 3.5 years one might be looking at roughly 9 submarines launched. In next 3 years another 9, in the following 2.5 years another 9 and in the next 2 years another 9. That's 36 submarines in 11 years from the first launch.
That may be the best performance case scenario. It's always possible actual production rates due to unforeseen events complicate the learning curve. Still, with that new building hall with two more sections being built - overall production rate from all 5 sections may eventually not only meet 36 subs in 11 years but go over it, by some margin.
Also, the single painting hall and launch dock might be an issue when both buildings and all 5 assembly lines are going full pace. That's five submarines per year being put in the water.
Looking back onto the commissioning rate of various nuclear submarines from Sevmash during the cold war, I can't help but wonder once the new Bohai facility is running on all cylinders, whether there might be a year or two where they're also able to achieve double digit launch of nuclear subs like they did with destroyers...
I think the whole point of having a dedicated painting hall is to facilitate a faster launch rate per year by virtue of division of labour -- most nations submarine construction just paint their submarines in the same location that they are assembled (i.e.: the Bohai equivalent of the eastern and southern assembly halls).
But they took the time to build a dedicated paint hall for SSN sized boats, meaning they feel like investment in that structure is worth it just to eke out that extra bit of efficiency, or they are expecting to launch quite a few boats per year to make it worthwhile -- or both.
The launch platform/pontoon won't be an issue; after all the time taken to launch a submarine is less than a day, all you have to do is wheel out a submarine onto the pontoon and sink it into the water and then put the submarine into the fitting out area, which is not exactly small.