Hi Wentsi,
Here's my answer. In order to import a list of contacts to the existing customers, You can check our blog (video tutorial) mentioned in link below as it guide you through how to import multiple contacts. in a very easy way.
http://method.me/cs/blogs/methodblog/archive/2014/03/27/importing-multiple-contacts-into-method-crm-tutorial-video.aspx
Moreover, you can also add contacts by simply going to the Customer Tab > Customer and ContactList Tablink> Select Customer > go to Conatcts Tab >Add contacts.
In this way you can add as many contacts as you want and you can give them Title as you need like deli manager and bakery manager.
In case you need more assistance feel free to post on our Forums.
-Inder