First of all you need to determine your server type. Plesk offers different type of licenses for virtual private servers and dedicated server.
And then you have three options for Plesk feature sets; Web Admin, Web Pro and Web Host editions.
Plesk Web Admin offers 10 domains limit and all basic features for server management.
Plesk Web Pro edition provides all features of web admin edition plus 30 domain limit, subscription management and ccount management. You will have access to developer pack tools as well.
Plesk Web Host edition has unlimited domain limit. It offers all features of Plesk Web Pro edition, plus reseller management features.
Do you have more questions? Do not hesitate to get in touch with us!