Is it decidable if there exists some input such that the TM makes at least five moves?
It's 9 because it doesn't matter what symbol we land on after move 5.
It's finite because the number of cells is 9, yes. The significance is because otherwise the algorithm in point 3 wouldn't finish.
All strings of length 9, with the starting point in the middle. "Five or fewer" is an error, I believe.