Crossword puzzle clue "set of answers"

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

Word that can precede each set of circled letters, forming a literal hint for entering certain answers in this puzzle

Set of answers

What's missing from the set of longest answers

It includes a vest ... and what can be found in each set of circles in the long answers

It may be set or set off

Box set set