Well I'd argue that there IS upkeep for characters, the simple fact of having to heal their injuries is "upkeeping", which made me think depriving undead of healing was a way to upset that.
Using my idea, big HP pool will probably steamroll the 2 or 3 first encounters following a lvl up, but afterwards things get trickier, since that pool isn't coming back up. Managing fatigue on the long run is pretty much the point of it all.
Leeching life to other party members seems interesting. But then again, it's pretty much the same as simply healing the character. Have the undead leech life on the toughest living party member, then heal her back up to full health with traditionnal methods.
I'd have no quarry with eating corpses but I'd feel there might be a missed opportunity to do something a bit different than usual. We don't get to play undead so often, but when we do, they're pretty much always the same.
