Dragos

I think a good approach would be to have 2-3 books already. Promote one for free or 99 cents with Amazon Ads and BookBub Ads and have it link back to your platform. The rest of the books on Amazon you would keep at the high limit of pricing near the $9.99 together with their print versions. On your platform you would give yearly access to all 3 ebooks for only $9/year (offering a 30% off for the first year). This makes it look like a great offer and should give better conversion rates.

Similarly to how Netflix works the more books you add, the easier it becomes to grow and scale. The bigger your library, the easier it is to attract and onboard new members and retain old ones. Even if you add a cringy version from time to time, people still see it as added value. They get more for the same price and you have more room to experiment and grow your craft.

You can implement this with WordPress and a membership plugin(ultimate membership pro on codecanyon.net) or some turn key solution like Podia, Gumroad.