That information can all be found by spending some time with Google. Most is answered in the X10 Technical Note that is available at multiple locations, including our own website:
http://jvde.us/info/X10_protocol.pdfTo handle 16 bit data you will need to use extended codes. There is another document for that, but it is not currently available on our website.
Quick answers:
1) Yes, on the same housecode: A1, A2, A3, A_ON
2) The dim commands must be concatenated with no gap between if you want to slew to a different level.
3) A1, A_Status Request -> A_Status_ON
4) Extended commands (you will have to read and understand the document).
Jeff