Questions about Using Two LG Ultrafine 5K Displays

[cloudyo]

I am planning to buy a second 5K Monitor. And I would like to know a few things about how they would work with a mac in practice:

1. What happens if I use the brightness controls on a magic keyboard? Will the brightness change for both displays simultaneously or only the primary one?
2. Is it possible to turn off one screen without disconnecting the thunderbolt or the power cable? Maybe through software? In an ideal world I could still use the USB hub on the back of the second display while the screen is off, but I guess that is wishful thinking...
3. Are there any (other) issues I should know about with this setup?

 

[konqerror]

Is this a Mac with a built-in display or not?

 

[cloudyo]

The mac has no built-in display.

 

[saulinpa]

1. Each display has independent brightness controls. You can hold down the control key to adjust brightness of the 2nd monitor. Or click on the desktop to change the focus first. Or use system preferences - displays for the slider.
2. SwitchResX used to be able to disable one monitor. I don't know about the current version.
3. Depends on what Mac you have. Unless yours is rated for 2x5K TB3 or uses a separate GPU then you may need TB3-TB2 adapters to make one of them look like 4K to the OS. Also the brightness controls may be quirky if both on the same GPU.

Note that the LG 5K has been updated so that the new version can use DP over USB-C.