Pre-Production for Video Essay

I am looking to make my first video essay to try and create a reel that I can use to highlight my editing abilities.

I plan to start with an idea and write a script around it, and being my first foray into Video Essays, I will look to keep it on the shorter side, 5-10 minutes. This isn't about getting views on YouTube and about practicing both editing and storytelling.

So once I have the script together, I need to pull visuals, but where do I start?

Should I pool lots of different media together first, or find stuff that fits what I am talking about as I get there, i.e the first 10 seconds talks about x and y, so I go find footage for x and y, fit it in the timeline, then the next 20 seconds talks about z so go back and find footage for z and chop it in.

What sites are there for this kind of media? (I am aware of Adobe Stock, curious if there are any other offerings out there or if it will depend more on what subject I am looking to do).

Really just how to get organised and plan out doing a video essay, any tips, tricks, or tales from experience will be greatly appreciated.

Thanks!