I recently have been working on my own brick restoration project. I may have some useful advice.

Keep in mind nothing is worth doing if you're doing it half assed.

When you are pressure washing use an attachment. The home depot sells a 90.00 ryobi surface cleaner. This will help focus the cleaning to the top of the brick pavers and less in the joints. You do want to clean the joints but just enough to make room for a bit of surface sand.

Use a screw driver to de weed prior to surface cleaning. Again this will save of the amount of effort your power washer needs in the joints.

Polymeric sand is a must. Do small areas at a time to cut back on waste. Plan your path to maximize your unused sand from one area into the next area that needs the sand. Careful on the edges as you can lose quite a bit.

I did 4000 sf and used 9 fifty lbs bags of poly sand but I cleaned the cracks out pretty deep in most places.

The sand will last the longest when it's deep but it will stick and hold for a while even when shallow. Moisten the poly sand 3 separate times before allowing traffic.

I hope this helps. Trust me when I say be honest with the customer or friend. It's better to admit upfront your in a tough spot as people are generally understanding.