Hi Gunnar,

You can set default value for any of field from selected form view. Just see the below screen. User can set default value from "debug" mode.

I hope this will help you.

Through the GUI I don't believe so. I don't see a way anyway. You should be able to do it programatically. 

The field you are looking for is the "type" field in the product.template model. It is originally defined in /addons/product/product.py. You can change it in that file, but it may not work since I think this column is inherited and changed somewhere else. Best practice is to create a custom module and inherit the model with this column:

 'type': fields.selection([('product','Stockable Product'),('consu', 'Consumable'),('service','Service')], 'Product Type', required=True, default='product' help="Consumable are product where you don't manage stock, a service is a non-material product provided by a company or an individual.")

Also, you will find information on the default fields in the ORM API docs for 8.0:

https://www.odoo.com/documentation/8.0/reference/orm.html#creating-models