Squee's controller chooses which player or planeswalker the Goblin token is attacking. It doesn't need to be the same player or planeswalker that Squee is attacking.

The casting permission granted by Squee's last ability doesn't change when you may cast it from your graveyard.

If Squee is countered or dies after being cast from your graveyard, it returns to the graveyard. It may be cast this way again later.

Once you begin casting a spell from your graveyard, it immediately moves to the stack. Players can't take any other actions until you've finished casting the spell.