Here a list of specs I found browsing the forum incl. source (no guarantee whatsoever though)
CPU supports three displays (laptop lid and two external via 1 x USB-C/DisplayPort 1.2 and 1 x HDMI 2.0)
You can look up max resolutions and refresh rates here to choose a matching monitor and where to connect it.
DisplayPort over USB-C can get a bit tricky if you use a hub since it might need to share bandwidth with a USB device connected to the hub. So if you want to connect a device using USB3 SuperSpeed to that hub you will only have two of the four DP lanes available, hence half the refresh rate or resolution. (Out of some reason you can either use 4, 2 or 1 lane - not 3 of the 4 available lanes) USB2 devices will use separate pins and shouldn’t influence video bandwidth.
Feel free to correct me or post additions.