I have been using SSRS since it came out for SQL 2000.
1. One of the questions asked for multiple queries per DataSet. In this, one query IS a DataSet, so the answer is no. Do not think of the DataSet as the same one in .NET.
2. If you want a report to automatically refresh, this is not possible without a call to the server. So, to simulate this, under the "Report Properties" dialog, check the "Auto Refresh" box and set your interval.
3. As for the RowNumber problem, I am not sure. Have you tried putting it at the row level and just changing what you need there? I have never had a need to do a matrix yet, so I am not sure. It would make sense why it wouldn't work since a matrix is not a listing of data rows.