When exactly do you consume the element for upgrading the movement?

The element can be consumed at any time during the movement - so before you start moving, after you move some spaces or after you move all spaces.

If an Add Target effect is applied to the card, it adds a single attack vs. a different target using the main ability values (which can be boosted if lightning is consumed).

[Errata] The bottom of the card should read "attack abilities" instead of "attack actions". Only attack abilities can be performed from the summon's position.

For the summon on the bottom, for any attack ability, you can choose to originate it on your hex, or the summon's hex, but not both. So something like "target all enemies within range 4" would target either all enemies within range 4 of you, or all enemies within range 4 of your summon. Keep in mind that you are still the source of the attack, so you would only suffer disadvantage on a ranged attack, or suffer the effects of a non-ranged retaliate, if the attacked enemy was adjacent to you. Also note this summon has no attack action or a base attack value. It cannot be commanded to attack with an "Attack +X" action, but it can be commanded to attack with an "Attack X" action (e.g. the Mindthief's "Possession").

The bottom is the only action in the game that does not have a base ability. Consuming elements gives you different abilities you can perform in whatever order you want. For instance, you could consume fire, wind, and ice to move 3 hexes, loot 1, and then perform the attack 3, range 3.