Thanks for your questions!
1) The spirit acts on its own like a summon and does not take the player’s action.
2) The spirit always stays in Close range of the player character. The Spirit Allies from the Mastery ability can move around though!
3) If the rules say that something “counts as a weapon”, it can have tags added to it unless otherwise stated (like for the Brawler’s Martial Art). Phantom Strike can have tags added, and any weapons wielded by summons can have tags added.