Comments - What hardware configuration I need for my sceneario?
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There is no difference between one server and multiple for the same resources. Databases within a server are quite de-conflicted from each other.
Cases for multiple servers (or instances within the same server) include security isolation (beyond user level privs). Global tunings required to be different per database. Different MariaDB versions required per database.
A single instances is a good way to start, and if any of the above cases arise a particular database can be split off to a new instance.
Hardware specifications will vary considerably depending on what sorts of queries you are doing.
With your existing databases I assume you have some measure of how much resources each use already?