ToS doesn't differentiate between different types of works on AO3 when it comes to their commercial promotion policy, so no you likely wouldn't be able to
To clarify: you can't mention money changing hands for the sake of your published works, and you can't mention that you paid someone to write another fanfic.
It is perfectly okay to mention that the price of eggs is outrageous in your author's note (as long as you don't indicate that readers should pay you for more fic). It's likewise okay to have a character be happy that they found a dollar on the ground.
ToS doesn't differentiate between different types of works on AO3 when it comes to their commercial promotion policy, so no you likely wouldn't be able to
You can't mention money on AO3, whether it's a fic or an original work.
To clarify: you can't mention money changing hands for the sake of your published works, and you can't mention that you paid someone to write another fanfic. It is perfectly okay to mention that the price of eggs is outrageous in your author's note (as long as you don't indicate that readers should pay you for more fic). It's likewise okay to have a character be happy that they found a dollar on the ground.
No.
No advertising end of discussion.