Thank you so much for your guide. But.. I just made a new installation of OS X Yosemite, and the first thing I tried to install after mamp was drush.
When I install composer I get some "permission denied" - "https://packagist.org could not be fully loaded, package information was loaded from the local cache and may be out of date" - anyone having the same problem?
When I try to "drush cc all" I get the warning: "No Drupal site found, only 'drush' cache was cleared. ". I have been trying to solve the problem for 3 weeks now, and i still haven't found any solution. Help is so much appreciated :)