Would creatures that are immune or have restistance to Necrotic attacks should also have resistance to "Shadow" even if Necrotic is not listed on the power? (example: Aura of Dread class feature)
No, Aura of Dread is a fear attack regardless of the power source, think of it as the equivalent of a cleric's cause fear attack.
Would it make a difference to change the Shadow power source to Arcane?
Not really, since currently power sources have little effects on mechanics... it influences mainly the fluff rather than the crunch. Keep in mind that death, undead and the like are strongly tied to the Shadowfell, makes more sense to use the shadow power source than arcane.
Implement suggestion: While the player is going with a wand, we we're wondering why not let something like a sickle (the other farm reaping tool) or a skull (treated in the same way as an orb), be also used as in implement?
Makes sense, id allow it.
Skeleton Minion: Would it be overpowered to let this power summon multiple skelotons at the same time as the player reaches certain levels (example 2 skeletons at level 5, 3 at lv11, etc) or have a feat that allows it too?
maybe a feat, id make it a paragon tier feat that allows two at 11th level and three at 21st level.
