Less than 750k in my case, at least 
But when I try again, this time without crashing the PoC environment, how many should I attempt at a time?
When my single CREATE SCHEMA_CHANGE JOB ran with the 750K ADD DIRECTED EDGE commands, I received no reply for ~48 hours, GraphStudio would not allow Design Schema nor Explore Graph for multiple graphs on the platform (just displayed the spin symbol), and further .gsql() calls from PyTigerGraph hung.
Thanks for any insights.