I'd get a cheaper case and better components. All the mobos listed are consumer grades. No server grades. I would suggest you pick the one with the longest warranty. Asus prime Z270-A is alright. IX Hero is overkill for your needs. Try to get a more recent gpu (Pascal). GTX 1060 or 1070...
A good 500 or 600 PSU from EVGA is more than enough.
I'm not a competitive gamer either so I prefer to play games at ultra settings (better visuals) at 60 fps rather than trying to get 144 with medium settings.
V-sync does the job. You don't need G-sync.
I have 3 x BenQ BL3200PT 32" 2560x1440. Resolution total 7680x1440 @ 60 fps
you can remove it using a microfiber cleaning cloths with hot water. its not the ideal but better than old thermal paste.
Just make sure there's no impurity before reapplying.