I filed for an extension on my 2018 taxes. What is the deadline for filing? And am I able to set up a payment plan since my Due is so ridiculously high??

I think in the end when you e-file, TT gives you an option of payment. And the last option in the bottom is Payment Plan setup with the IRS 

The extension gives you until Oct 15 to file.  Efiling is open until Oct 15 midnight then it closes.  After that you will have to print and mail your return.

But that is only to file the return.  Any tax due was due on April 15 so Interest has been accruing.  Did you send in a payment with the extension?