I need to create a really large print of 4Mx2.5M. I've never designed such a large print and I need help in setting the right DPI for this. I am really clueless of how this is supposed to go. If I'm not wrong, this needs to be split for few different documents, right? What DPI should I set?
How far away is someone going to be looking at it?
Typically the larger the printer, the further away the user is going to be looking at it, so the lower resolution that you need.
At 4m x 2.5m, that sounds like a small billboard, so anything over 72dpi is likely overkill given that people will be 20 meters away looking at it.
(but, in the end, consult your printer)