We hand invited the publishers that join our market because, as your question suggests, there is some threshold between who should and should not try direct sales.
There are no hard rules, just guidelines.
The superseding one is this: Do you have inventory (audience) an advertiser would take the time to specifically work with you for? If you open a "store" and starting selling this stuff, do people want to buy it?
One measure is traffic, but that's not enough. In general we like to look for sites with 100,000 page views a month or more.
But it can depend on the content and vertical. For example, we power a website that gets 25k hits a month but is the only site covering the voice over talent industry in Hollywood - so its super nichey and there is a market for those advertisers.
Other examples of small but successful premium properties include some hyperlocal ones (www.queensmamas.com, www.brooklynheightsblog.com, www.brokelyn.com, etc), the largest blog for truckers, largest blog for prison wardens, etc.
The conflicting examples are sites with large traffic but bad audiences/verticals. We reject a lot of "tech blog" also-rans that just copy and paste content from TechCrunch but get a lot of SEO traffic from it. Or even if it's a legit site, it can be in a bad brand-advertiser vertical like home finance / mortgages (which is mostly lead gen advertisers)
it depends, in all reality you should ask this to potential investors... as they all have their own criteria. in my experience it has always been 5k to 10k users or dllr amount. that's when your startup shifts from idea validation to growth (emerging business) and pitching becomes easier and more realistic for most angels... the projection again is best to make relations with investors (if that's your goal) so you know what they look for... before you actually need to pitch them... hope it helps a bit ;)
Critical mass cannot be achieved instantly in any case. Success is only possible for those who work hard, work smart and stay vigilant in the market. This has been the most widely used indicator for measuring a company’s achievement of critical mass. In reaching critical mass, however, missing that target revenue stream is the difference between future growth and frustration. To ensure that critical mass is achieved, the entrepreneur must have measurable goals. These goals can be as simple as determining the monthly revenue needed to be self-sufficient, or as complex as determining the number of new clients each salesperson needs to engage. Celebrate each client or sale that brings the company closer to critical mass and encourage the employees to cheer each other on as well. Often overlooked, one of the important indicators of a company’s preparation for critical mass is the strength of its early adopters. By capitalizing on the unique relationship early adopters have with your company, reaching critical mass can happen quickly.
You can read more here: https://www.cleverism.com/critical-mass-complete-guide/
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath