What do you want to know about them? I think it's just a matter of concentrating and seeing how many sensations you can sense at a time, and what their qualities are, etc. Experience will show you the way.
This topic might also be fundamental only to MCTB-style Vipassana, and not other Buddhist schools.
Alan Smithee:
1) that no two sensations can occur simultaneously (hence, the finger trip exercise)
This might not be absolutely true. If you try to experience two sensations at once, 'attention' will bounce between them, ping-ping-ping, in a stressful way. What happens if you try to do that, but see what's 'underneath' the ping-ping-ping between the fingers? Try to experience the fingers at the same time, but not by focusing harder + harder, rather, subtler + subtler.