Is it even possible (I'm not asking now for how-to) but only givin question: Is it possible to make e.g. Full Armor with one item (like you have only legs in pack, and when dropped on player it equips full armor: legs, tunic, leggings... and uses all layers so player can't wear on it another leggings; and is possible to equip only if player is naked (or simply doesn't have some objects equipped).
yes, this is possible.
In the CanEquip method of the armor, you would check the other layers to see if anything was equipped.
In the OnEquip method you would add the other pieces of the armor set.