After you file

Yes, you should enter the Total Amount of 'Other Education Expenses' you incurred in the Education Section.  TurboTax will calculate the $400 needed to qualify for the American Opportunity Credit, and include the balance as Qualified Education Expenses. 

You are correct that if your 1099-Q Distribution does not exceed Qualified Education Expenses, you don't have to include it in your return, but definitely keep records of your education expenses.

Click this link for more info on Reporting Form 1099-Q.

Your can review the Education Tuition and Fees Summary to see the calculations (screenshot).

Use FORMS mode in TurboTax Desktop, or the Print Center from the left-side menu in TurboTax Online.