2) You will not need to "point" your project to your DDT profile becase the DDT profile will contain the deployment data packages to gather the messages when a new package is created for the DDT.
3) When you set the solution preferences to point to a specific project, the localization type editors will search within the project for a key matching the key and/or value you specify. Once the "LocalizationKey" property is set on a control, the control will retrieve the appropriate value at runtime for localization by searching with the localization store for the text value matching the key that is set as the LocalizationKey property.