Making of a channel

I need to answer 5 technical questions before I start making the channel

1. What does asterisk need from the channel? (What are the bare minimum features/functionalities of a channel?)
2. What all can asterisk take from the channel? (What is the largest possible set of features/functionalities that a channel can support out of the box?)
3. What are the features of the channel needed by the customer?
4. Is there any feature that a normal asterisk channel cannot support or it is very difficult to support?
5. How to add support to a new feature in channel?

I am searching the answer for the first question now.