Well...from a power standpoint...the torpedoes simply require a compatible launcher.  They don't really require any more power.  As for the armor plating....the generators work similarly to replicators.  Once the hull armor is created, it requires no extra power.  It's a physical barrier rather than an energy shield.<br/><br/>As for what the ship is.....I think that StarFleet has had some fundamental changes in thought process in recent history.  Between having to fight off the Borg Invasion (book canon) after the Dominion War along with what happened with Voyager (a long way away with no backup), the way the Fleet builds it's ships has changed.  While they build exploration vessels....they make sure that the ships can defend themselves especially when they may be going out on their own with no hope of support (speak softly, but carry a bit stick mentality).  We've established that the McNair has higher power output capabilities than a lot of other ships.  I don't see this being a problem.