Benthic Anomaly's triggered ability will resolve before Benthic Anomaly does. If Benthic Anomaly is countered or otherwise leaves the stack in response to that triggered ability, the triggered ability will still resolve as normal.

If the copied creature has {X} in its mana cost, X is 0.

Devoid doesn't affect the color identity of the card for the purposes of the Commander variant. For example, while Abstruse Appropriation is colorless because it has devoid, its color identity is still white and black, and it can't be included in a Commander deck where the commander's color identity doesn't include both white and black.

Other cards and abilities can give a card with devoid a color. If that happens, it's just the new color, not that color and colorless.

If the copied creature is itself a token, the token created by Benthic Anomaly's ability copies the original characteristics of that token as stated by the effect that created it, with the listed exception.

If a card loses devoid, it will still be colorless. This is because effects that change an object's color (like the one created by devoid) are considered before the object loses devoid.

The token is an Eldrazi creature instead of its other types and subtypes and is colorless instead of retaining any of its colors. It retains any supertypes it had, such as legendary or snow. These are copiable values of the token that other effects may copy.

The token copies exactly what was printed on the original card and nothing else, with the listed exceptions (unless that creature is itself copying something else; see below). It doesn't copy whether that creature is tapped or untapped, whether it has any counters on it or Auras attached to it, or any non-copy effects that have changed its power, toughness, types, color, and so on.

Devoid works in all zones, not just on the battlefield.

If the copied creature is copying something else, then the token enters the battlefield as whatever that creature copied, with the listed exceptions.

A card with devoid is just colorless. It's not colorless and the colors of mana in its mana cost.

Any enters-the-battlefield abilities of the copied creature will trigger when the token enters the battlefield. Any "as [this creature] enters the battlefield" or "[this creature] enters the battlefield with" abilities of the creature will also work.