ExternalStorage is a module, you need to copy it to your project folder and add it in the IDE with Project/Add Existing Modules.
DropBox is an additional library, you should copy the DropboxV2.jar and the DropboxV2.xml files into the \AdditionalLibraries\B4A folder.
No.
Not all librairies, manly older ones, are managed do not have the Online version.
For all 'Internal' libraries do not worry, those are automatically updated when you update B4A.
For 'Additional' you can either click on the Online link to get to its forum page, or you need to search in the forum.
Did you also update the AdditionalLibaries field in Tools / Configure paths ?
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