How to improve on this Facebook group strategy?

I have a new fb group where I plan to sell my targeted niche ebook and video course. But first I wanted to know if it’s possible to pay like a Microworkers site for people to join the group while it’s public and like then post a provided post usually in a form of a pre written question then I have the moderator answers all the questions .

The goal is to get about 800-1000 members in the group using this method so it can catch some momentum. Then I’ll change the group name so it’s more relevant to the niche topic.
After that then turn the group to paid private group where new members will have to purchase the $17 ebook before being approved to the group.

Is there any other website or even forum posting sites where I can pay users a few cents to post and like in the public group?

Test it with running an ads first. If it works, then scale it up.

Even for a paid group run ads?
By me changing the name of the group I know for a fact it will receive interest due to the niche. I have a cvs of 15 groups totaling 156k people

At first I had a VA add 2,700 group members and users Id to csv, only to find out that fb disabled targeting users via user id.

I just would like for all the people who come from paid ads to be once the group name is changed and the group already has many members on the inside. Giving the new targeted people a reason to want to pay then join the group