Starter plan is always free, and there is no time limit, you can use it as long as you want.
Yes. To upgrade, sign in and go to your account settings, and in the billing section, choose the plan that works for you.
You will not be charged when you cancel your plan anytime during the trial period.
Your card will be automatically charged when the free trial ends, and at the start of each term until you cancel your plan. Your plan's term starts at the end of your trial period.
Cancel anytime during the free trial. Sign in and go to your account settings, and cancel your plan.
No. The Starter plan does not require a credit card. You only need to have a valid email. If you already have a Google or Facebook account, you don't need to enter name and email, just hit the right button and you're signed in!
Yes. You can only receive payment after the trial period ends.