how can i tell if device is rated for 5v or 3.3v ?

amine2:
my question is whether or not it can slide on the surface . because the connector is in the middle of the board and not on any of the edges .

They will (normally) fit flush, but it depends on the wires used and other stuff nearby.

But as I am sure you were going to do a trial component fit (see post #20) you can check at that time if the wires are intefering with other stuff.