Well, it's hard to say for sure. Sometimes a Touhou comic might stick closely to certain expectations, while in other cases it could take some creative liberties and deviate.
Sure, you can. Just make sure the videos don't violate any copyright or community guidelines of the story platform. Also, consider if the content is still relevant and engaging for your audience.
In my opinion, the story of Flandre Scarlet is also a great one in the Touhou series. Flandre is a powerful vampire who has been locked away for a long time. Her story is about her isolation, her struggle with her own power, and her attempts to interact with the outside world. It shows her complex personality, from her child - like innocence to her terrifying strength when provoked. This contrast makes her story very engaging.
Well, start by familiarizing yourself with the Touhou characters and their backstories. Then, plan out a simple storyline that fits the Touhou universe.
One way is to look on dedicated video-sharing platforms and filter the results by date. Also, check out specialized archives or collections related to the type of story you're interested in.