what happens if I send short or long press of power button when the computer is already on? would the computer reacts as if I pressed the physical power button when it is already running?
Yes and no, this depends on the case of your pc.
Normally short press is the default on and off for legacy, long press off means force shutdown power off.
On some cases a short press means a forced reboot, especially not on windows.
I got the same layout however to me short press doesn't really work, it doesn't reboot for me it instead just powers off which is weird because my direct case buttons work as expected.
The restart button does nothing for me.