Answers to planeswalkers are always great, and you cant underestimate the value of a good beater
Feather, Radiant Arbiter is the backup commander, thought as cool as the card is, it doesnt really match the theme of the deck
(Again, this is explained in further detail in my column on the design of double-faced cards.) The road to the Werewolf mechanic began not down the design path of double-faced cards, but rather down the path of designing the day/night mechanic
If you do, investigate twice
You could build a deck filled with mono-black assassins, or a deck that uses lots of morph, manifest, cloak, and disguise creatures