Invisible Stalker is what I need to have to put Ethereal Armor on, spirits are great but they wont have hexproof unless there are two Drogskol Captains out, I know Invisible Stalker seems out of place but because he is not blockable he gets around opponents flyers and since he has immediate hexproof he cant be removed without a board wipe. It works out really well because opponents are forced to use their removal on Drogskol Captain, Mindshrieker, etc. It works, it helps play around protection too because the people I play with use creatures with Pro-white or Pro-Creatures. It really helps win the race. Having more spirits would be great all at once but they can be blocked by other flyers.
I've considered building something like this more than once. I like it. Invisible Stalker is an auto-include in this deck because hexproof and unblockable make him the best creature to put the pants on...only way to get rid of him is with a sweeper.
Phantasmal Image would be good here I think. You can copy either Drogskol Captain (to protect both Captains) and or Invisible Stalker.
Like the idea! You might include a few umbras like a Hyena Umbra to protect you from wraths... :)
Also, Azorius Herald and Flitterstep Eidolon cant be blocked, and Eidolon of Countless Battles is a spirit and an enchantment. Eidolon of Rhetoric will stop storm dead. Kataki, War's Wage will assassinate affinity. Guardian of the Guildpact will ruin a mono colored decks day. Kira, Great Glass-Spinner protects your creatures. If you have one (its expensive) Geist of Saint Traft is quite the spirit bomb. Sorry if I overwhelmed you with suggestions, but I am working on a deck like this too right now. :)