I suggest you go ahead and amend your 2017 return and mail it. You can go ahead and transfer the 2017 amended data into your 2018 return when you start it and go ahead and complete it. You can wait until near the Oct. 15 deadline for filing a 2018 return with extension.
If your 2017 amended return isn't processed by then, go ahead and file your 2018 return in the hopes that the IRS will not make any changes to your 2017 amended return. If the IRS processes your 2017 amended return before Oct. 15 and does make changes, you can make any changes to your 2018 return caused by the IRS changes to your 2017 amended return before you file it.
If you expect to owe any tax on your 2018 return, you were required to pay those estimated taxes when you filed for the extension by April 15. If you didn't you will be incurring underpayment penalties the longer you wait to file.
