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?
Why not do both advertising and affiliate?
I don't know what website are you going to make since you didn't mention it. But if it's a regular website, then you can put advertisements to it. That's how most websites make money anyway. There are some that even put pop up videos for advertisements.
If you're going to build a website that's about gambling or whatever as long as it's an article/reviews, put your referral code on whatever website are you giving reviews.
The amount of money that you'll get from both depends on how much traffic would you get and how much people would click the links. I wouldn't expect that much at first since there's a lot of websites that share the same niche. You're just starting out and there's a particular website on whatever niche you have that already has regular visitors. Don't expect them to just move to your website.