Hi Ramon,
EC is probably not geared for multiscreen, but here's some things that happen with the GUI.
Top screen is a 1920x1080 monitor, the bottom screen is my laptops 1366x768.
It doesn't matter what configuration the screens are, the results are the same.
Starting EC when the GUI crosses screens - the module gui's are corrupted

Here's the module gui when starting EC on only 1 screen. From here I can expand it across screen borders with no problems

It's not a problem, but it might be something to consider later.
;)