No special setup is needed, just make sure that database structures are the same on all the computers and use the same MySql version. You may use SQLyog's data structure sync tool to ensure the first criterion.
You'll need SELECT, INSERT, UPDATE, DELETE privileges to all tables to be synced.
300k databases are small, even a dial-up connection would be sufficient, although a simple DSL or leased line would be a more reliable method. Whole databases will not be copied (apart from the first sync), SJA uses concat_ws() to generate a checksum for each record to be compared.
SJA is scheduled by OS' built-in scheduler tool, once you are convinced that the sync does what you had expected, then you can leave the job alone.