You should use section headings, I am told. Your entire manuscript is a set of five-page essays, divided into chapters that are subdivided into sections. Thinking from the ground up, that is a set of five-page essays.
At one per week for 50 weeks that is five chapters of ten sections each, for example. This is a very interesting way to think about it. I tend to find section headings awkward, but I may change my mind.
Axé.
coldhearted scientist وداد 
You can use them and then suppress them in the final version if they no longer work for you. A longer chapter needs them (more than 30 pages).
Yes, but I tend to find the piece either lends itself to having them or does not. I don’t like to write with them and then suppress — write with storyboard yes, but in sections no, unless the piece falls into them naturally.
BUT, that is on the theory that the section is just a section. If one thinks of the section as a freestanding, finished piece, it is a different matter and I am much more interested! 🙂
Yes. It can work to have the sections be autonomous in a more real sense. I am just saying that even if you do it that way you can still decide later to make it a more seamless piece.