Create one-off page with specific fields and template
Use the Empty Page module and create an empty page.

Just like node content types, you can create a custom block type in /admin/structure/block/block-content/types

Add fields to your block type, and then in /admin/structure/block/block-content create a block of your block type. 

Place block in content region and for Visibility > Pages put the URL for your empty page, so the block is only visible at this page.