In fact, because many squares are defended only once, you have such possibilities as 1. e4 e5 2. Bc4 Bc5 3. Qg4; the disadvantage of developing each piece is that it no longer does the same work it did when it was at home.
In 3D Chess, each Pawn is defended by 3 or more pieces: the Pawn at 4f7 is defended by the King at 4e8, the Commoner at 5e8, and the Commoner at 3e8.
The problem of f7 is, simply stated, does this change the "feel" of the game so much that it does not deserve to be called "3d Chess"?
There is no certain way to answer this short of playing some number of games, but one can at least try to answer the question.
We could start with only one chess-set worth of pieces, but then there would be too much empty space compared to the number of pieces.
It wouldn't be chess, but we could allow limited multi-piece 3D moves: for example, 1. 4e2-4e4 4e7-4e5 2. Qd1-h5.
In the above example, the three Queens from 3d1, 4d1, and 5d1 are moved as a unit; they cross paths on 4e2 and land on the appropriate h5, that is, Q3d1-7h5, Q4d1-4h5, Q5d1-1h5. If you insist that there can be only one crossing square, then no more than 3 pieces can be moved at a time. This is probably a good variant (and a new invention), but it isn't chess.
Although 4b7 is defended three times, and therefore won't be hanging until you develop the all three Bishops, from 3c8, 4c8, and 5c8, it is still true that you will want to develop all three.
After 1. 4e4 4e5 2. B4f1-4c4, the square 4f7 isn't attacked strongly yet; but when you develop B1f1-4c4 and B7f1-7c4, it is attacked as often as it is defended, and you still have 5 more White-squared Bishops to use. In order to reach this state of equilibrium in attack and defense, you had to develop 37% of your White-squared Bishops, whereas in FIDE Chess, you had to develop 100% of them.
By this argument, it is possible that the attack is even stronger in 3D Chess than it is in FIDE Chess. What's more, you can attack not only 4f7 but also 3f7 and 5f7: total defense of the 3 squares is 5 pieces, so the attack ratio starts to get interesting, especially because a Q at 3h5 attacks both 3f7 and 5f7 with a 3D fork.