Choosing the correct monitor is very important as it doesn’t help you have a beast of a computer and not having a monitor that does the graphics justice. Also keep in mind how much graphics processing power the screen will need. For example a P1080 (144Hz) requires the same or even more power than a P1440 (60Hz) 2K screen. If you don’t want to spend a lot of money on a Graphics Card then don’t go for more than P1080 (60Hz). That being said the stunning visuals of a good 4k P2160 monitor is something to experience. Keep in mind that even with a GTX 1080 you will not be able to set all games to max at P2160.
If you are looking for a monitor it is also important to know what games you like playing the most. For example if you’re really into first person shooter games and you’re looking for every advantage then it might be better to go for a faster refresh rate (144Hz instead of 60Hz) and free sync for AMD or G sync for NVidia (the reduce screen shudder between frames). If however you are more into real time strategy games where it really doesn’t matter rather go for a high resolution screen such at P1440 or P2160.