For easy sanding, a little bit talc will be useful. Do not forget, the specific weight of the microballoon is far more less than any other component, so use as much in the mix, as possible. (For this reason, use as thin resin, as you can do. Sorrowfully I do not know non-professional name, or availability of a good, thin aerospace resin: Huntsman (CIBA) Araldite LY 5052 and its hardener.
As a working safety engineer I must draw your attention: do not touch resin (mainly the hardener) by bare hands. Some plastic or surgeon gloves must be weared.
As a thinner*, or to wash instruments, acetone is the best, neither alcohol, nor some thinner can work properly.
*when you work with some foam (white, blue or pink) you can work with only methanol. However, after work, far from foams, you can wash the brushes only by acetone...