It is a Tax Law thing that you must take the entire $25,000 if you are able to.
It is an Tax Law thing (or possibly an IRS thing) that it is too late to "waive the carryback" on a 2016 tax return.
Yes, you need to amend 2014 to use the NOL.
If you do the calculations and you are sure that the NOL will NOT be used up by amending your 2014 and 2015 tax return, yes, you can file your original 2017 tax return with the proper NOL. However, it is possible the IRS won't fully process it because they see an unexplained NOL. As long as you need to go through the calcuations to determine what the NOL is, you might as well file the 2016, amended 2014, and amended 2015 tax returns. However, as I said before, if the NOL will be fully used on your your 2014 and/or 2015 tax return (do they have at least $25,000 of income?), the NOL does not affect your 2017 tax return, and you will be fine with filing your 2017 tax return.
Considering your large number of questions and the fact that TurboTax does not calculate the NOLs, you may consider going to a tax professional.
