BAPI and backend Webdynpro model classes

Three basic questions:

1. Does it have to be a BAPI for backend connection or any remote RFC-enabled FM will do?

2. Do I have to map all the (BAPI's) FM's import and export parameters into the model relations and their cardinalities or can i pick and choose the ones that I'm after? If so, how do I know which are essential and which ones I can ignore?

3. Between the wizards and the plethora of objects that need to be created and linked what is the most consuming aspect of configuring (I don't think anyone would want to write code for all of them) a backend webdynpro?