few questions about adding water

Adding water to my first rr setup. Couple of questions.....
I have an aqueon 65 RR tank... Does water only go into the over flow from the top or will it get in from bottom and middle? In other words can my tank be full and over flow be dry?

Should I wait till sand settles to fill all the way up and open over flow and turn everything on?

How long can the live sand last without circulation?