I am building an acoustic guitar and have reached the point where I have to "finish" the guitar.  It has a walnut back and sides which I need to fill before applying a  french polish finish.  The walnut has an open grain and there are several suggested approaches to filling it.  West One 105/206 epoxy resin is popular.  But I'm rather taken with glasscast 3 for its self levelling and clarity properties.  It would be applied with a squeegee (old credit card) very thinly and then flattened with increasingly fine abrasive to achieve perfect flatness before applying shellac.  So my questions are:-
1.  Is it suitable for use as a grain filler in the way that I've described?
2.  Is it Ok to sand?
3.  What might be the drying time for a very thin coating?
4.  Are there other considerations that I should bear in mind?
Thanks in advance.
Bikergordy
Arthurian Guitars