If you're not super heavy into PC gaming, don't do it yet. 1440p with higher frame rates is your friend. To utilize a 4K monitor with high fps, you need hardware that either doesn't exist or simply costs so much that it blows your budget into the stratosphere. A decent 4K monitor alone will cost more than any console, or an entire decent PC. For 1440p though, I'd recommend either 27" or even 32", I'm currently using a 32" display and it has served me well for many years. You can get a really good 1440p monitor for a fraction of the price of a 4K panel.