I read in that post about nudging events shortcuts (and usefull possibility indeed).
What is “start left” i.e. alt+left supposed to do?
I thought it would take the event to project start, but it just moves left by a step, the same way as ctr+left ( ? ) How can I achieve the former?
What about up/down? Can I assign shortcuts in order to move events from one channel to another? That would be handy too!
Please enlighten me!
Nudge>Start Left nudges the start time of the event leftwards by the current quantize value, without affecting its end position. This is different than Nudge>Left, which moves both start and end.
That other thread was not about moving events, rather the question was about moving tracks up or down. In Cubase, tracks are not events.
You can assign hundreds of commands. Please look inside the Key Commands dialog. 
What about up/down? Can I assign shortcuts in order to move events from one channel to another? That would be handy too!
In Keycommands, you have the 2 commands in the folder “Nudge”:
“Up”
“Down”
With these 2, you can move a selected event in the Project WIndow up or down, 1 Track at a time.