Mapping how and where

According to what I have read, when the data is ingested it receives a default text value. At this moment I am in the task of mapping to define the correct type of the fields since for example "src" has "text" type.

This process of defining the name of the fields according to the ECS (Elastic Common Schema) do you recommend me to do it from the .conf file? or should I do it directly from Kibana using API Rest to define the types by means of a JSON?

Is there a table to guide the field mapping process? I would expect that when applying ECS I can use the available use cases and dasboards so I want to make sure to use the correct names for each field according to ECS.

Thank you in advance for your valuable help.