If, for some reason, the permanent doesn't have the squad ability when it's on the battlefield, the ability won't trigger, even if you've paid the squad cost one or more times.

If the spell is countered, the squad ability will not trigger, and no tokens will be created.

Tokens will be created for each of your opponents, not just opponents that you attacked.

The tokens created by the squad ability aren't "cast," so any abilities that trigger when a spell is cast won't trigger for the copies.

Although the tokens created by the last ability are attacking, they were never declared as attacking creatures. Abilities that trigger whenever a creature attacks won't trigger when those tokens enter attacking.

You may pay the squad cost any number of times. You will create a token that is a copy of that permanent for each time you paid the squad cost. If you paid the squad cost multiple times, the tokens will all enter the battlefield simultaneously.

If the spell resolves but the permanent with squad leaves the battlefield before its squad ability resolves, you'll still create the token copies.