Be careful aiming for sound isolation, it can be counterproductive.
Generally speaking "sound isolation" means reducing where sound can escape from the case, and putting some noise absorbing foam where you can to dampen the noise.
The counterproductive part is that having a lot of airflow would be the opposite of "sound isolating" -- anywhere air flows freely sound does as well. So by definition a sound isolating case has poor airflow. Poor airflow could require you to run your fans at higher RPMs to compensate, which is then introducing more noise than you would have had with a more open case that could run low RPM fans.
Back when the P180 was new, its silicone grommets for HDD mounting and the thicker multi-layer side panels (instead of flimsy pieces of sheet metal) were highly unusual features.
I'd say they had reasonable airflow, with 2 120mm fans on the front (one in the main compartment, one in the lower compartment with the PSU and HDD). Though the intake fans were behind a door with vertical vent strips up the sides. I'm sure that restricted airflow a bit, but it was dramatically quieter than any case I'd had before.
My personal one was the slightly revised P182, but I'd previously built some computers at my job that we put in P180s.
No idea - I remember spending a lot of time browsing Silent PC Review on previous builds to make sure I got an appropriately quiet power supply and everything else, but it stopped doing any meaningful testing years ago, and the current incarnation basically looks like affiliate link blogspam.
That's still my case, but it's huge and I don't need that space anymore.