A sealer is a softer (easy to sand) coat, so I normally use only one coat of sealer, then build with the "real" finish. (Of course there are always exceptions, but the "normally" applies to one coat.)
For something like the outside back of a bookcase, I might have no final finish, or just one coat after the sealer - just enough to make it smooth and impressive - not collect dust.
The insider back of the bookcase may only have a couple coats total - it shows, but no wear, so just finished enough for appearances.
The outside and sides of a bookcase may have 4-5 build coats or more, because of potential wear. Generally I do a light sanding before the final coat, to be sure I have a perfect surface. Then the final coat. If it is a "modest" gloss finish, I rub with 1000 then 4000 Abralon. If it is a "fine" finish, I sand with 400 then go finer until I get the degree of gloss I want, sometimes using wet sanding, sometimes dry, sometimes with rubbing compounds.
If I need an exceptionally hard surface, I have recently been spraying 1-2 coats of a water base conversion varnish on top of the lacquer build coats.
Does that help?