In theory, you can do something like that with Peertube, it's a federated alternative to YT.

In practice, serving video content requires fuckloads of bandwidth, which has huge costs. The first thing you'll want/need is to limit filesizes and/or video resolution. Depending on what you start with, how much initial money you have, even allowing people to watch everything in 720p might be a strain.

For paying the costs with ads, unless you can guarantee hundreds of thousands of daily views, the platforms won't be willing to pay much, "low exposition" or whatever. Though, if the only thing that won't be there is hate speech and dark web, you're letting normal porn in, which can drive significant traffic, but now you'll have to deal with puritanical companies not wanting to associate with your site, plus companies afraid of the possible backlash.

Ideally, you'd have to create your own ad server, so you'd have to reach out to companies directly and ask them if they'd like to advertise on your platform with no middlemen.