I run https://officesnapshots.com https://officesnapshots.com and we sell and self host our own advertising and have experience with this concept. Even before

I run https://officesnapshots.com https://officesnapshots.com and we sell and self host our own advertising and have experience with this concept. Even before building any tech, I would say the most important thing would be to find a website and try to sell ads for them. You could then add some html to their site to test the concept and build some trust with both the publisher and advertiser. If the publisher uses Google Ads, see which advertisers already spend money to advertise on the site and approach them directly to buy a month of ads at something like a 25% discount. 25% off is less than they were paying, but 75% is more than what Google was paying the publisher.