I have used both the poly design and epoxy system over the years. Both have their advantages.

Honestly I don't sand much at all with either system. My methods are below.

Polyester resin method:

I mix my resin (sig finishing resin) this way: 1 ounce resin, 1 ounce MEK, and 20 drops of hardener. Yes most brands say 10 drops. Mix the resin and hardener first, then add the MEK.
Using a 1 inch camel hair brush I then brush the resin on the cloth. Start in the middle and work out. The consistency of the resin is more like milk. You should be able to glass one side of a wing panel in about 5 minutes. Once done, clean brush with MEK and do another panel.
This stuff dries in about 30 minutes.
Next dry sand the cloth lightly to take the glaze off with 220 grit garnet paper. Do not wet sand. Apply another coat of resin the same as the first.
Let dry and dry sand once more lightly to take the glaze off with 220 paper.
Brush on 2 coats of primer and let dry. I use PPG K-36 personally.
Normally I could do a set of wings and stabs in a day from bare wood to primer. This was back when we were building BVM jets on a regular basis.

Z-poxy resin method:

Mis resin per instructions.
Spray the cloth with a light coat of 3m77 spray adhesive and lye and work in place on part.
Pour a small bead on the cloth beginning in the middle . Using a playing card squeegee the resin all over the part.
Once it is fully covered, continue to squeegee all resin off. You should be able to touch the surface with dry fingers and not stick to it at all and get almost no resin residue on your fingers.
When dry, sand with 220 garnet dry lightly.
Repeat the resin procedure as above to include the primer.

I prefer e poly system as it is faster, but does smell. If you can handle the smell it is the answer.