I sanded after the first layer of fabric and after filling in the depressions. Seems like if I keep this as smooth as possible in between steps that I'll minimize sanding. So when it was smooth I vacuumed and cleaned it for the next layer of fabric.
Next day I applied the remaining 4 layers of glass to the canopy/skin. I used the same process of brushing on a layer of liquid and fabric and finally covered the whole thing with peel ply.
What a mess. Everything is throw away in this process.