Gandorfin

I'm using gtx 1080 with freesync monitor and it works really well there is this fan made list of some fressync monitors and how well they behave with Nvidia G-Sync compatible mode https://docs.google.com/spreadsheets/d/1Ej9mOe5NamLldpfyFfXrqvLMZP-aG2Zi1su7QzPRNJY/edit#gid=0 it also list min and max frame rates where freesync works on each monitor some have rather high ranges like 40-144hz others less ps. other list I haven't checked yet but it seems to have some different screens tested https://www.esportstales.com/tech-tips/list-of-nvidia-gsync-compatible-freesync-monitors-tested-by-community

I'm in group of people who are rather unimpressed with 144hz I notice the difference when I actively try to but it's just "meh" for me I'm definitively getting more "wow" from higher resolution and screen size rather than 144hz so I recommend checking things in person before bying and yes I set it to 144hz in nvidia control panel

probably LG 27UK650 out of these two it's pretty good 4k monitor

you still will get some extra air to gpu because psu shroud is perforated look at GamerNexus review of phanteks p400a it also has perforated shroud and 3x120mm was better than 2x140mm for gpu temps (you should take also in account those 3x120mm were weak stock fans while 140mm were Noctua's)

I would go with three 120mm fans It's better for cooling gpu along with cpu rather than just concertinaing on upper half. Tbh. I would go with some other fans with higher static pressure than Noctua NF-S12A like for ex. Arctic BioniX P120 PWM, SilverStone FQ121, Fractal Design Venturi HP-12 PWM, Enermax DF Pressure (this has really good stats on paper for both airflow and static pressure though how good is in practice idk?). Or if you want to spend more money you could go for Noctua NF-A12x25 one of best fans on market or Nidec Servo Gentle Typhoon (over 2000rpm variants) those are superb top tier fans. The higher static pressure helps push air better through rather restrictive mesh filter and it makes quite a difference in Meshify C.