Horace comes to propose but never gets it out because (through Dolly's meddling) Cornelius and Barnaby (his clerks at his store) are there and Horace believes that Irene is dating one of them.
14Dolly sings a song about not wanting what, to pass her by?
Answer: Parade
Dolly is referring that she better get busy making Horace realize that he loves her before it's to late (hence the title "Before the Parade Passes By").
16What do Cornelius and Barnaby have to do before they leave New York?
Answer: All of them
They do all of these things. They spend every nickel they have. They almost get thrown in jail by Miss Irene because of them hiding in her store. Cornelius kisses Irene and Barnaby kisses Minnie Fay.
18What does everyone come to get from Horace Vandergelder when they get back from New York?
Answer: Money
Everyone wants their savings that Horace was keeping in his safe. Cornelius and Barnaby want theirs to buy the store across the street, and Ermengarde wants hers so she and Ambrose can use it.
19What's the name of the "heiress" Dolly sets Horace up with?
Answer: Ernestina Simple
Dolly used this to distract Horace from marrying Miss Molloy because she knew he could rather marry someone rich and famous (Ernestina was supposedly a rich heiress).
20How do Cornelius and Barnaby close down the Hay and Feed Store so they can go to New York?
Answer: explode cans of chicken mash
Cornelius and Barnaby put lighted candles under the cans of chicken mash. When the cans heated, they exploded and "would cause such a stink it would keep customers out for 24 hours."
Dolly asked Gussie right after she was done telling Horace about the date. Dolly knew Gussie would act terrible so she could come in and take Mr. Vandergelder.
23What's the sign Dolly's been waiting for from her late husband Efrem Levi.
Answer: The Forest Green Shutters
She says toward the beginning that if Horace had any sense he'd paint the shutters green (this was said after Horace left for New York); so when Horace says that he's having the shutters done in green it's the sign Dolly's been waiting for to go and marry him.