You choose which player, planeswalker, or battle the token is attacking. It doesn't need to be the same player, planeswalker, or battle that any of the other Goblins are attacking.

If General Kreat enters at the same time as one or more other creatures you control, its last ability will trigger for each of those creatures.

Although the token created by General Kreat's first ability enters attacking, it was never declared as an attacker. Abilities that trigger whenever a creature attacks won't trigger. If there are any costs to have a creature attack, those costs won't apply to the token.