Dual Monitor Recommendation - 1080 + 4k side by side?

for your environment i don't see any issue. Since 4k monitor will reduce the scrolling and you can fit more window for video editor app. For programmer like me, it was bad choose for me to get 4k, since i didnt look the dpi when it comes to text (too small to read) forcing me to get another screen. Also, if you like to turn off your screen while it rendering the video, you need to make sure the hdmi support 4k since displayPort will always rest your window when you turn off screen.