I added another deck to the top of the saucer section. I also added the impulse engine. The bridge will probably be directly on top of the piece that holds the impulse engine where it goes up onto the saucer top. I’d thought about adding another deck there and having the bridge on top of that but then the ship would have looked too “stacked” for my taste.
Right now the ship has 6 decks but it will gain at least two more (possibly 3) when I add the bridge and another part to the bottom. I don’t count the nacelles, which would actually add a few more decks.