Rate MUST be wet, on meter, to avoid problems.
Depends on the aircraft - The group I used to be in you could leave the front tank full which gave (IIRC) about 3:30 flying with no W&B problem, if you wanted more you could then put some in the rear. We charged dry and left it full - if you got back late, a note was left and the next person filled the front and it was charged to you - worked well for us, but no good if you cannot be sure of the fuel level.