Mainly FPS, Fallout 4, Witcher Wild Hunt and of course World of Warships and War Thunder
24 inch is the largest I would go as once you hit the next form factor you start needing to up your GFX's, as soon as you up your GFX's, it's as well going for 4K ...
Dvi-D rather than HDMI as it handles the higher refresh speeds, HDMI is okay for console fanboys but not for decent systems.
Again going Display Port would mean a change of GFX card p.
Would also be TN rather than IPS monitor, costs and refresh rate come in to it.