I've been reading some of the other posts here on the forum regarding CIM but still have some questions:

1) Am I correct in thinking that I should have only one CustomerProfile for each for each of my customers?  Does the authorize.net system prevent me from using a single merchantCustomerID more than once?  There was a post on here that referred to a duplicate profile error returned by the authorize.net API but I have seen no information to tell me under what circumstances that would occur.

2) Is a credit card or bank account number required when creating a CustomerProfile? The CIM documentation neglects to explicitly specify if this information is required, optional, or conditional.

3) Is it possible to look up an authorize.net customer profile using merchantCustomerId?  Looking at GetCustomerProfile, this does not appear to the case.

4) While I find the PDF documentation for CIM linked here to be pretty useful, it is pretty narrowly focused on the inputs and outputs of the API.  Is there a more general source of documentation to show the ins and outs of CIM -- perhaps an overview or tutorial-based documentation?

5) What is the difference between SOAP and XML guides?  If I'm using the PHP code provided by authorize.net, do I even care?  From what I can tell, there is no way for me to specify whether I use SOAP or XML.

6) Where does one specify the web service location when setting up one's PHP code?  The documentation refers to Production, Test, and WSDL variants without describing why one would choose one or the other.  Additionally, all urls contain 'soap' in them, suggesting they might be inappropriate for an XML implementation.

7) In some of the AIM code examples, I see definition of such constants as AUTHORIZENET_API_LOGIN_ID,  AUTHORIZENET_TRANSACTION_KEY, and AUTHORIZENET_SANDBOX.  Is defining these in one's own code the proper approach to configuring the authorize.net PHP code?  Are there other such constants?  Where is this configuration documented?