There is a specific amount of grease you should shoot for, not completely filling the cavity. I wouldn't go nuts trying to match it, but that and the procedure for adjusting the play should be followed. Do change the seal, but I would only change the bearings if they are damaged or worn. This is the best guide I have ever seen describing common bearing failures:
http://www.bardenbearings.com/scan%20pdf/Bearing%20Failure%20Brochure.pdf
Also, you can wash the bearings out in kerosene and then a little rubbing alcohol before blowing them dry and greasing them, but do not use the air to spin the bearing cage around the race.