MySQL by default witll run as the user specified by my.cnf, if at some point in the future you want to run mysql as your user you can change that on ´my.cnf´ by adding the following lines
user=USERNAME
Or if you want to add it as a startup option to mysqld or mysqld_safe
--user=USERNAME
Also the default permissions for directories inside the mysql data directory (this is in Linux, but it should apply to the Mac version too):
- 755 (rwxr-xr-x) for mysql top data directory
- 700 (rwx------) for each database directory
- 660 (rw-rw----) for database files