I only received a single state coupon to mail in. Are there supposed to be more docs - federal coupon, instructions, etc.?

If you are referring to an Indiana Post-Filing Coupon see the excerpt below from this Indiana webpage:

 

Do I have to mail anything to Revenue if I file electronically?

• If you will receive a refund, you do not need to send in anything.
• If you owe the State and decide to make not to pay online, you will need to print your return. The �Post Filing Coupon� is attached to the print out of your return. Detach the coupon and include it with your check for the total amount owed by April 17th to avoid late fees and penalties.

This is just an Indiana issue. There are no Federal coupons.

 

If you are getting a refund, or you pay online, you don't need the coupon.

 

Indiana is one of several states that doesn't allow for direct debit payments on the tax return. This is a state issue rather than a TurboTax issue.

 

The state does accept online payments on their website.