Hello Jordana,
1) "Our coffee is known for its sweet, slightly acidic taste."
* If you can put an and or a but between the adjectives, a comma most likely belongs there.
2) "There are a little under twenty days until Christmas."
3) "There are a little over 30 holidays in the winter."
*Holidays is plural, so you need are instead of is here.
Good luck!
Brandy Caulfield