I'm in a similar boat. The first few weeks with my 16" MBP was pretty bad. Everything seems resolved now,
except the issue with the discreet GPU kicking in when an external monitor is plugged in. This, in turn causes the fans to spin up (which is annoying when trying to code).
My 2017 13" MBP (without discreet GPU) was barely usable when powering my 4K monitor but at least it was quiet. It makes me think that the more modern integrated Intel GPU in the 16" should be enough to power my monitor without fan noise. Sadly, Apple has decided I can't have that option.