I have created a Datasnap Server that access various databases. You can have Pooled connections to the databases. I personnaly use devart SDAC components to access the databases. But I think pooled connections should work with Firedac.

On each Datasnap method that access a database, I instanciate a connection to the database. At the end of the procedure, I free the connection. In this scenario and with pools activated, the number of real connections to the db will NOT be huge. See https://docwiki.embarcadero.com/CodeExamples/Sydney/en/FireDAC.Pooling_Sample