Multisite for e-marketplace

Hi, I’m building an e-marketplace (domain.com) where users, after registering, can have their own space. Each customer will have configured a subdomain (client.domain.com) with the chosen theme. Do I need multiple licenses? All subdomains will have the same graphics

No, you don’t need multiple license if you manage this via an extension or DNS configuration.
( If you install the system/theme on one domain, no need )