Would love to know the best way to go about creating the following widget dynamically:
Well, creating the widget is not the problem. The question is, how do you define those “must read” (do I really?) posts? If you want it to be dynamic, I guess you want to do this based on category or most read or whatever.
Ideally, I’d want to make able to pick posts from within the panel instead of hard-coding them through my text editor.
And yeah, creating the actual widget was not super tough 
You could use a structure field somewhere (site settings, separate page) with a select field. So you can add as many “Must Reads” (I really hate such categories 
) as you want.
Another option would be a checkbox field within the posts themselves, but that’s probably less comfortable.