For static screen integrated graphics watching web pages and You Tube, pick the one with the features and look you like best. Many of the lesser expensive monitors will be Free Sync, so it leaves you in a nice place for an AMD card which are also less expensive to boot. Beyond that, having a "good" monitor for your use case can be very much dependent on what you are playing as well. If you do a lot of single player games then framerate tends not to matter nearly as much as eye candy. If you are going to play competitive online games it is almost always better to go with high framerate at the expense of eye candy.
I saw your repost just before posting my reply. That prebuilt is not going to be a good candidate for a graphics card unless both small enough and efficient enough to run inside that system. Where I have no specific experience with that exact build, I would also venture to say that a standard power supply isn't going to fit either. Otherwise, as above.
Edit- I found this system on WalMart and it is indicating there is a HDD in this unit? Something that would absolutely make this a better user experience would be to at least update to an SSD. IDK if the motherboard has the connection for an M.2, but either of those would make this FEEL much better, smoother experience even on the desktop. Convert the HDD to bulk storage.