Here's my method that I have been using since 1977 (almost 35 years):

Phase 1)
3 coats of WELL-MIXED and STIRRED Aero Gloss Balsa Fillercoat with sanding between coats 2 and 3; coat two should be applied over coat one as soon as the solvents flash in coat one.
Sand coat two after an hour and apply coat 3.
After drying at least an hour, sand coat 3.

Phase 2)
After the sanded balsa fillercoat has dried overnight, apply two or more coats of Aero Gloss Sanding Sealer over the fillercoat, with sanding between coats after they dry.

Some apply the sealer before the fillercoat but that is BACKWARDS as the fillercoat FILLS much better over the raw wood.

Finished wood parts using this method can be topcoated with ANYTHING including butyrate dope. Using Elmers Water-based fill-n-finish results in a substrate NOT compatible with dope or "hot" solvent content lacquers. In addition, fill-n-finish makes a HIDEOUS DUST MESS when sanding which Aero Gloss products do not.

__________________
When in doubt, WHACK the GAS and DITCH the brake !!!

Yes, there is such a thing as NORMAL, if you have to ask what is "NORMAL" , you probably aren't !
Failure may not be an OPTION, but it is ALWAYS a POSSIBILITY.
ALL systems are GO for MAYHEM, CHAOS, and HAVOC !