1. Yes you need the PRO version for SSL
2. SSL certificates are basically the same (although there can be different types such as code signing certs). It doesn't matter what vendor you use, although generally you want one that is what's called a root certification authority.
Generally you get a certificate that has your hostname set to the 'Common Name' attribute of the certificate, and that is used for validation.
3. To validate the server, you use a server certificate on the server to ensure that you are connecting to the correct server. That's the most common use of a certificate in SSL.
You can also give each client a certificate, and validate each client (instead of say using a password).
4. Look at the "How to use FTPS" examples at this link
http://www.enterprisedt.com/products/ed ... howto.html