That placement would be also fitting for use with TV, though I guess that could be reserved for other uses...
Some 27" 2560x1440 would be good starting point for monitor.
Also those don't need paying arm, both legs and half the internal organs for graphics card.
And I guess you would be also using headphones.
Do you have those or need new?
Beyerdynamic DT770 would be good very reasonably priced closed design headphone.
32 ohm version has p/leather pads with higher environmental noise isolation if that room is noisier.
Though those also insulate heat better than velour padded ones.
As for case I assume also that should be discreet without RGB bling bling ADHD look.
So would this style look good?
https://www.overclockers.co.uk/fractal-design-define-nano-s-mini-itx-case-black-ca-074-fd.html
Fractal Design is about only maker using proper mass damping material in side panels.
For CPUs few months later timing would have given lot better bang per buck with choise being now "Damned if you do, damned if you don't":
You either pay serious overprice for something with currently better performance...
But which isn't going to stay as high end for long and doesn't have upgrade path.
Or then take CPU clock speed limited by originally Samsung's phone/table CPU manufacturing tech...
And upgrade CPU to made on more modern node than Intels and with more processing power for the future.
(engineering sample demoed in CES to match 9900K's processing power at ~50W lower power consumption)
Anyway for CPU cooler Scythe Mugen 5 would be very powerfull for reasonable size and should fit most cases without PSU above CPU.
https://www.overclockers.co.uk/scythe-scmg-5100-mugen-5-rev.b-cpu-cooler-hs-046-sy.html