1)  I've seen it done both ways.  Personally, if I'm going to develop well-written and well-defined use cases, a laundry list of "system shall" statements is redundant and a wasted effort.

2) Again, I've seen it done both ways and to various extents.  It all depends on the needs of the organization and/or the project team.  I tend to get involved in the pieces of design that deal with user experience, but I know some BAs who have deep technical skills and do database and architecture design.

3) I'm getting repetitive, I know, but yep I've seen prototypes developed in many different stages of construction.  Some are no more than drawings (literally, on whiteboards or paper) and some are high-fidelity using tools like iRise, and others are actual code that needs only tweeks and "prettification" to go to production.

4) Sorry, but I haven't the time at the moment to address this one.  Maybe I'll come back in another month?  LOL