If you use the Zinsser shellac, make sure to get the Seal Coat or decant the others. They contain wax.
You can buy dry dewaxed shellac flakes from Homestead Finishing, Shellac.net or a slew of other places.
The dry flakes are awesome because you only dissolve what you need and you can adjust viscosity to suit the project, not to mention the different tones available.
I use pumice powder, diatomaceous earth or talc mixed with tung oil as grain filler. They all go transparent. Just like any other paste filler, let it haze over and wipe with burlap. Those powders also double as rubbing compounds