What are ALL of the necessary steps to allow more user accounts to be made?

In addition to paying the $1/month fee for additional 1,000 users, must I also pay for more space on the data tables to allow more than 200,000 users? Are there any additional fees or extensions that I must do?

Also, what happens if my user number hits its limit and someone attempts to create an account? Will it just fail to create the account or is there a way to put it on a kind of “auto-renew”?

Thanks in advance.

$1/month for additional 1,000 users is old information, there is no limit on the users now.

The Users table is not limited, but all other table allow up to 200,000 objects for free. You can expand the storage by buying a Function Pack. All limits for the free tier are documented here:

If you have not purchased a function packs, server will respond with an error. Once you purchase a function pack, there is an option to auto-purchase additional pack items on as-needed basis.