Validate idea with paylink - your experience?

Hello indies,

i'm trying to validate several ideas with a landing page and have a paylink (stripe).
What i mean by that:
I'll like to have a cta button on the page, where a user can buy a spot on a waiting list.
Then, after enough users have purchased a spot, i start building the product.

So here are my questions:

• Who of you has successfully used this technique? What was your product, how did your page look like (do you have pictures or even still a live page) ? / what was the workflow?
• What are your conversion rates?
• What were your traffic sources? What works best?
• How expensive was your product or spot on the waiting list? Did you charge for the full product on saving the spot or just a small amount?

Looking forward to your replies!