- How the heck do you set the thing to development in the config file?
See http://doc.silverstripe.com/doku.php?id=debugging for more information on how to set debugging errors etc. You just need to add this command to your mysite/_config.php file
As for deletion of all your data, if you followed the instructions above you should have only 'emptied' the members table and rebuilt it with the user accounts as the second step. You should have not lost anything apart from the current member accounts. You may have hit 'Empty' when you had selected the database rather then just the 'members' table? which will empty everything!
Of course when your messing round straight in the database it pays to be doubly sure about what your doing!