MariaDB slave replication server from many sources?
I don't know about "500", but there is "multi-source" replication in recent versions of MySQL, plus MariaDB.

So that is 500 inserts per minute on the Slave?  8/second is no problem.  Even 1 core would not be taxed.  Even if all inserts went into the same table.

Even if multi-source did not let you have 500, you could put, say, 25 instances of MySQL on a single server, each receiving data from 20 Masters.