You can assign a template to a folder and define default metadata for the contained documents. This is configurable in the Ext. Properties tab of the folder's settings panel.
Here you can select a template and configure default values for each custom attribute, click on Save to confirm the modifications. Whenever someone insert a new document, its metadata will be pre-filled with the ones you have defined at the folder level and proposed to the user.
Each time a new document will be added, it's metadata will be taken from those you specified at folder level and proposed to the user.
If you want to constrain all the contained documents to be associated to the same template, select the Template locked option.