I have an idea for a website that will attract many visitors.
I will need to put a lot of effort to build it,
but then it will run (almost) by itself.
What will be the best way to convert it to some passive income?
Advertising? Affiliates? VIP registration?
How much should I expect to earn from it?
The first thing that you need to think is how to promote your site after it's online. It is the hard part for every site owner because they need to attract visitor day by day. And if they can do this for at least three months, then they can add some advertising like Google Adsense or something like that so the site will give some profit for you. Affiliates can work if you can find a good product that many people were looking for and you can use any affiliate website to choose the product.
It is difficult to say how much you can earn because it depends on how many visitors that come to your site and click the ads in that site. But I know that one website that has thousand visitors can give a nice profit at the end of the month so you can make passive income especially if you do not stop to promote your site.
I think passive income is overstated. I do not believe any money you make is passive at all. Even real estate where people think you just simply collect rent from others is not really "passive" in a way. You still have to find people to rent your space and you still have to make sure you are getting paid by them and they are not late every month.
Now that is of course less work than most other jobs but it is still work and it puts your income in jeopardy if you do not follow up on that. The only passive income I know is putting your money into savings and just let it incrementally rise up there but even that's too little to worth anything.