Tips or Tricks: Identifying if there are Opened Documents New Mac user here, trying to figure out how to adapt my workflow and the like from Windows/Linux to Mac.

I think the answer might be "it's not possible" but here goes anyway.

I'm used to leaving documents open as a reminder to complete them later. This means I'm used to quickly glancing at the taskbar (dock) to determine which documents I have open and what I need to do. Since the red x doesn't actually close a lot of apps - terminal for instance - it makes it a little tedious to determine if I have an open document.

The only solutions I can think of are either remembering to manually ⌘Q-ing each window (oof), or to right click each open app to determine if there are opened documents and then remembering the answer. Neither of those are great so I'm wondering if anyone has any good methods around this.

I realize this might encourage discussion/opinions, but I'd like to emphasize that I am looking for concrete answers EG: "there isn't a way" or "This setting will make the number of opened documents be displayed on the dock". One of the biggest issues I'm having with moving to Mac is determining the best way to solve a problem, and I'm guessing that what I think is a solution here might not actually work.
Just by looking the taskbar I think you can't. But you can set an easy shortcut and if you click on the application you want to view and the press the shortcut you can see all the windows opened (active and minimised) for that application. 

In System Preference > Mission Control, you can set a shortcut for Application windows. Just try it once and with time it will become smooth for you.