I wish to make a deductible contribution a Traditional IRA for 2016. Must I purchase the IRA before filing, or can I use my refunds to purchase the IRA before 4/18/17?

You don't have to open the IRA before you file, but if you are claiming a deduction for the contribution it will need to be made by the due date of the 2016 return.

If you file, claiming the deduction and then change your mind, then an amended return would be required to correct your return.

As long as you expect to receive the refund (or you can fund the IRA with other funds) before the due date of your return, you can go ahead and file now.