4. Grade 25 balls, probably uses either 18 or 22 1/4" balls.
5. I'd lay the new axle in the drop outs and see if it's too long before installing. QR axle cannot protrude beyond the drop out or it won't clamp. A mm on each side, I'd probably use a grinder to shorten and the advice to thread on cone/nut to clean threads still applies.