You will want to buy new seals and cotter keys. If the brakes are old it is cheaper to buy complete backer plate assemblies rather than buy the magnets and shoes. One source is Trailer hitch, hitches and bike rack (800)298-8924
As for packing the bearings. Have a good means of cleaning them first, parts cleaner if you can get to one or gas and a paint brush. Just make sure you get all the old grease out. Put a small egg size glob of grease in your left hand and with a folding into the grease motion force grease into the larger end of the bearing until it shows out the top. Rotate the bearing and repeat this action till grease has worked its way out the top all the way around the bearing.
Put the large bearing in the hub. I like to lay a little extra grease on the top of the bearing before setting the seal, don't fill it up. Place the seal in position and with a block of wood on the seal tap the seal in until the wood bottoms on the hub.
Put a light coating of grease on the spindle. This is more a water proofing on the areas of the spindle that is not in contact with the bearing.
Place the hub on the spindle, place the outer bearing trust washer and nut on the spindle. Tighten the nut with a pair of channel lock pliers while spinning the hub till the nut is tight. Back the nut off a half turn and tighten it again with your hand. The hub should have slight in and out movement when you have tightened it by hand. Over tightening is the wrong way to go. The nut should end up one or two notches back from the pliers tightened position, depending on if you have 6 or 12 notches in the nut. Once the nut is set slip in the cotter key and fold it back over the spindle and set the cap on by tapping it into place with a cold chisel working your way around the flange. You will feel the change when it bottoms on the hub.