1. Was there any promotional content in this game, such as pre-order bonuses, special DLC codes, possessing save data from a different game, and the like?
2. Is there anything permanently missable, such as needing to fulfill specific requirements while playing the game to unlock something?
3. Is this game identical on all platforms, including the Switch version having an in-game achievement equivalent?
4. Is mayonnaise an instrument?

I know I am late but:
1. There was a physical release with a bunch of extras but they are not digital or relevant to the game. The only DLC is the costumes pack available on GOG as well. If you pre-ordered you'd get it for free.
2. No, not to progress the game. That is what in my opinion makes this game better than BFBB, there are no colletables required to continue with the next level. You do not to collect coins in order to unlock new teirs of cosmetics that do not influence gameplay.
3. Only the controls and graphics differas far as I know.
4. No Patrick, mayonnaise is not an instrument.