I’d recommend you consider getting above a 750W power supply- don’t see that listed in the build but thought I’d mention. 750 can be cutting it close with a 3080 and K series. I have a 1,000W and while performance is only marginally better my CTD have drastically reduced. I used to not be able to make it through a whole flight.
As others have said go with the 32GB RAM. Yes- you will be getting near top performance compared to other systems. It should be good timing too as hopefully some of the performance issues will be ironed out. You have a top end processor and a 3090 would only be marginally better. You can look into AMD too and they’re great, but MSFS favors single core speed at the moment.
I have a very similar setup and performance is still very hit or miss until they fix the engine. The airliners stutter heavily and drop frames all the time. I think that will be resolved though.