PostgreSQL to MySQL migration to use database for WordPress site - how to's?
Any specific reason to migrate to MySQL?

https://wordpress.org/plugins/postgresql-for-wordpress/

Else MySQL Workbench will work. You'll always have to take into consideration any functions/triggers, etc. that might contain advanced pgsql syntax, etc.

http://mysqlworkbench.org/2012/11/how-to-migrate-postgresql-databases-to-mysql-using-the-mysql-workbench-migration-wizard/

As @Max said, good luck!!