No and No
Soul Feast is a free action.
While a creature is unconscious, it is helpless, it can’t take actions, and it takes a -5 penalty to all defenses. It also can’t flank and is unaware of its surroundings. When a creature is subjected to this condition, it falls prone, if possible. See also helpless and prone.
Soul Feast grants Temporary Hit Points. Temporary Hitpoints, while useful to a dying character, do not raise the character's HP above 0, though they may mitigate the effects of ongoing damage or subsequent enemy attacks.
Temporary Hit Points:
Not Real Hit Points: Temporary hit points aren’t real hit points. They’re a layer of insulation that attacks have to get through before they start doing damage to you. Don’t add temporary hit points to your current hit points (if your current hit points are 0, you still have 0 when you receive temporary hit points). Keep track of them as a separate pool of hit points.