If Starting Town enters during another player's turn, it'll enter tapped no matter how many turns they've taken.

A creature attacks alone if it's the only creature declared as an attacker during the declare attackers step (including creatures controlled by your teammates, if applicable). For example, Squall's first ability won't trigger if you attack with multiple creatures and all but one of them are removed from combat. Similarly, creatures that enter the battlefield attacking later in combat won't be considered when determining whether or not a creature attacked alone.

Starting Town's first ability cares about how many turns you have taken, not necessarily how many turns the game has had, in case you take an extra turn.

If a card in your graveyard has {X} in its mana cost, X is 0 for the purpose of determining its mana value.

If an effect restarts the game, Starting Town will enter tapped in the new game unless it's your first, second, or third turn of that game.