[PDOException]
SQLSTATE[HY000] [1045] Access denied for user 'forge'@'localhost' (using password: NO)
You need to set up your environment variables.
From forge, go to manage your site. Click the "Environment" tab and then set the Key/Value pairs for your application.
For example 'key' = DB_HOST - 'value' = Your server IP address.
DB_NAME - forge
DB_USERNAME - forge
DB_PASSWORD - the database password that was emailed to you
... and so on.
With regards the API key, if you use the DigitalOcean (2.0) option when creating the server, you are not required to enter the API key so can ignore it.
The SSH key from Bitbucket should probably be entered when you set up the Git option (in Forge). I can't quite remember the process and would need to set up a new server to see that again.