Crossword puzzle clue "answers briefly"

How many letters are in the longest answers in this puzzle - or how many of these answers there are

Letter appearing only in down answers; its opposite appears only in across answers

Coolers, briefly, that span two words in the nine longest answers

Summer coolers, briefly, and a hint to this puzzle's six longest answers

Résumés, briefly, and a hint to this puzzle's eight longest answers

Provider of answers, briefly

Scholastic mean, briefly, hidden in this puzzle's seven longest answers

GroupMe exchanges, briefly, and a hint to this puzzle's eight longest answers