So everything was working fine. Now when I create, or try to create a new Slave site I get a blank /index.php page. I can refresh the page to continue but I get "This site already exists" and the Slave doesn't work or connects/creates the SQL. Is this fixable and how? Thanks in advance!!

Blank page is the symptom of a PHP fatal error somewhere that might be due to a permission problem or an extension or plugin or we don't know what.
To get more info on the potential fatal error origin, check if you have a "error_log" file that might provide more info.

Concerning "The site already exists", that mean that you already have create the same site ID or that a directory with the same name is already present in the "/multisites" directory.

As long as you have not create the slave site successfully, it will not be available.