Frontline Heroism

The copy created by Frontline Heroism's last ability is created on the stack, so it's not "cast". Abilities that trigger when a player casts a spell (like Frontline Heroism's own ability) won't trigger.

Frontline Heroism's last ability resolves before the spell that caused it to trigger. It resolves even if that spell is countered or otherwise leaves the stack without resolving.

You can't choose to pay any additional costs for the copy. However, effects based on any additional costs that were paid for the original spell are copied as though those same costs were paid for the copy too.

If you cast a spell that has multiple targets but all of them are the same creature you control, Frontline Heroism's last ability will trigger. In that case, the copy's targets will all be the token created by the ability.

The token that a resolving copy of a permanent spell becomes isn't "created" and won't interact with abilities that care about tokens being created, such as the first ability of Doubling Season.

Any choices made when the spell resolves won't have been made yet when it's copied. Any such choices will be made separately when the copy resolves.