To validate your idea you need to show interest from potential students.

To do that you need to show them something to be interested in. However, a teacher isn't going to go out of their way to create content for a site with no students waiting. To get around this issue, I would start off by getting a bunch of existing content that you can collect and curate on your website. This is how you do that:

Go to YouTube and Instructables (and similar sites), and spend a week searching through videos and instructions, collecting all the best content you can find. Try to get ones that are good, but are not universally recognized already with millions of subscribers/viewers. Then

A) Contact the creators of that content, telling them that you're starting a new website and you'd like to embed their content to attract new students. Tell them that you'll be tracking the popularity of their videos and the most successful teachers will be invited to be instructors on your future (more developed) website, with some special offers (e.g. lower % of their profits go to you). Also tell them that you will not be making any money off of the initial Beta-validation version of the website that you're currently building, it's solely to start attracting students.

B) If as you reach out to these teachers you find a big negative response (e.g. 90% say no and then set their videos to not be embeddable on external sites), then stop telling the teachers, and just use their videos. You won't be doing anything immoral, because you won't be making any money off of your initial Beta-validation website anyway. And when you launch your more developed site you can still reach out to the creators with the most successful videos on your Beta site.

To add some unique added-value to the embedded content, you could maybe even somehow couple your own additional clarifications, etc. with the content, to clarify things you feel they didn't fully explain, etc.

As you start getting students visiting your site and watching videos, make sure to be collecting email addresses so you can do a drip campaign to keep them coming back for content you suggest. As your student visitor # starts increasing you can also slowly start reaching out to teachers (either the ones from YouTube, and others from Udemy, etc.) to get more content created specifically for your site.

If you'd like more detailed advice relevant to your specific ideas I'd be happy to help,

Lee