As someone just getting started with MySQL, what should I know that you do?
Discussion
I chose MySQL 16 years ago when Postgres was still a bit too immature and was lacking the replication features that I needed at the time.
Now, Postgres is a much easier choice than MySQL.
Just one MySQL example: it reuses auto_increment values that were used but deleted when the server restarts. That is supposedly fixed in version 8.0, but it has been broken in all versions before that since 2003 including a version (5.7) that doesn’t reach end of life until this October.
If you have related child records that don’t get deleted when the parent record gets deleted and the foreign key is based on an auto_increment column, you can end up with child records pointed at new records that got assigned the old parent ID after the server restarts.