I've only had personal experience with a few monitors, and it's really one of those cases where personal preference, and how your own eyes feel about it, are the deciding factors, at least when it comes to size vs resolution.
However, the APU is not very powerful, so, while you can get a better video card, that will allow for more details, higher resolutions, or both, if you're going to be doing serious gaming, you'll likely want a whole new platform (modern Ryzen, etc).
What is your intended use case? If gaming, which games are you hoping to play?
Also, please, get a better PSU - right now, your system isn't very demanding, but Cooler Master does not make good power supplies. See the first link in my sig for recommendations.