Crossword puzzle clue "starting four"

Angle irons graphically represented by four sets of black squares in this grid, and by letter formations starting in the four longest answers

Starting a project ... and what the letters between the starting and ending pairs of letters in each starred answer are doing?

Collection consisting of four plates, four saucers, four bowls, etc.

Starting four

Super Bowl champions who appeared on Wheaties boxes four times, starting in 1993: 2 wds.

"I'm starting to enjoy this," or a hint to the sequence at the ends of the four longest answers

City where four presidents and four vice presidents served as governor

Skeletal parts, four of which can be found in rows four, seven, nine, and twelve