#2: Yes, of course, if you indeed don't want to allow duplicates.
#3: Silly to worry about NULLs in unique keys if you simply disallow NULL in your fields, which in that above case you clearly will be doing (for all fields, presumably).
Have to leave for the day. Will think on the others.
An optimist sees the glass as half full.
A pessimist sees the glass as half empty.
A realist drinks it no matter how much there is.