Spray-on shellac is certainly recommended by quite a few luthier types, and is compatible with just about all finishes. In theory you don't need more than one coat of shellac, but that may depend on how smoothly it goes on. Non-water based filler may be better for not shrinking than water based. Otherwise you may be best to allow for some shrinkage and simple wait a full month after the colour coat goes on before sanding that back flat, and then do the clear coats.

Lets start with the basics and what is the body wood?