If you don't use studio, you will need to use Nuxeo IDE or generate a maven project to build your bundle alone.

1. You can override the subject vocabulary defined here. You can ask to override the contribution there. Think to add your csv files to initialize your vocabulary as your wish. Or you can modify the vocabulary into your instance in the Admin Center without development.
2. yes you can drag a list of document from your desktop (with Firefox, Chrome or Safari - as HTML5 is needed) and let your list dragged over the target container into your browser waiting that bloc move from blue to green, and select import with metadata. See here about documentation.
3. There is no simple way without studio. Otherwise with Nuxeo IDE.

Yes I don't use Studio because it's expensive for an Proof of Concept … ! For the override I don't understand what you mean ?? How I can do it ? (PS : The right link for me is : http://explorer.nuxeo.org/nuxeo/site/distribution/Nuxeo%20Platform-5.6/viewContribution/org.nuxeo.ecm.directories--directories , i'm on 5.6 Nuxeo.)

Or you can modify the vocabulary into your instance in the Admin Center without development. … yes you can drag a list of document from your desktop and let your list dragged over the target container into your browser waiting that bloc move from blue to green, and select import with metadata

It's the way I choose and look like the more Easier.

@Mathhieu Guillaume : The answer is not realy clear for me … :/ ! Can't understand. (Maybe because some thing miss, or because my english is not enough good…)

If it's not possible with TAG is not an trouble if I have another way to do it.

Thanks you.

For the first point, you may want to check this question & answer.