Sacrosanct Wilderness (Keeper of the Forbidden Wilds)

Does an "or" line on a power divide the entire card?
No. The "or" line only applies to the clauses immediately above and below the line, without extra whitespace.
For example, if you use Crops Wither and Fade, you always gain 2 fear and then you may choose whether you are replacing a City or a Town. On the other hand, on Tormenting Rotflies, you either choose everything above the "or" or everything below it.
To be explicit, the following cards have clauses that are not part of the "or" choice (separated by whitespace): Crops Wither and Fade; Growth Through Sacrifice; Sacrosanct Wilderness; Gift of the Primordial Deeps; Gift of Flowing Power; Call to Guard; Vanish Softly Away, Forgotten by All; Thickets Erupt with Every Touch of Breeze
(Discussion elsewhere) Tags: Crops Wither and Fade (Shadows Flicker Like Flame), Growth Through Sacrifice, Sacrosanct Wilderness (Keeper of the Forbidden Wilds), Gift of the Primordial Deeps (Serpent Slumbering Beneath the Island), 15 more...

Must Gather/Push effects which don't say "up to" move exactly that many things? Eg: Does Fields Choked with Growth move exactly 3 Dahan?
Yes, if possible. If a card gives a number of pieces to move, you must move that number if you can, or as many as possible if there aren't enough of those pieces there.
Most "move some Dahan" powers represent the Spirit asking/working with the Dahan or calling in favors. A few, like this one, are more "the Dahan decide to get the heck out of Dodge". This applies to other kinds of pushes, as well.
Other cards with similar wording are Terrifying Chase (Sharp Fangs behind the Leaves), Sacrosanct Wilderness (Keeper of the Forbidden Wilds), and Twilight Fog Brings Madness.
(Discussion elsewhere) Tags: Gather, Push, Fields Choked with Growth (A Spread of Rampant Green), Terrifying Chase (Sharp Fangs behind the Leaves), 2 more...