giant sperm whale is 15x15x15 if a dwarf is 1x1x1
Or perhaps more realistically proportioned 28x11x11 or so.
The REALLY scary thing is that a giant moose is like 4x4x4 or something.
Except square is NOT the size of a dwarf, it is larger. Otherwise, you could only fit one dwarf in a square, and you would not be able to fit a wheelbarrow in a square if it had a dwarf stuffed into it. A square is AT LEAST twice the size of a dwarf.
Yes, so what? dwarves aren't cubes and sdwarves need airspace to move.
Neither are moose, and so do moose. So if a dwarf needs a square 2x as big as it to stand in, a moose needs a set of squares 2x as big as it to stand in also. So it cancels out on both sides of the equation when you're calculating things relatively, as we are doing here. If a dwarf needs 1 tiles to stand in freely and easily without falling over other dwarves (which is the case), a giant moose should need about 4x4x4 to stand in freely and easily.
do archers gain a bonus to range when higher up and if so, do they get a range bonus from step ladders?
No, despite there being parabolic arcs in game for other things, bolts fly in straight lines still only like lasers or something, so your range is actually decreased by going higher up.