How long is the free trial, and how is it different from the free Starter account?

The trial account is usage based rather than time based. It lasts at least 14 days, and depending on how you use the system it can last longer. When the trial is used up it expires, and you upgrade your plan to keep going.

The free Starter account is different: it does not expire, and it does not include sub-accounts.

To see what you have left, go to Settings, then Billing, then the Usage tab. Certain services show how many uses remain, and the AI assistant and agent credits show how many are included, how many you have used and any free credits that were granted.