Why not Kingmaker? The premise is that you've been send south to form a buffer state between the kingdom of Brevoy and the lawless, bandit-filled River Kingdoms. A necromancer wanting to found a kingdom where necromancy is legal and where they are the eternal lich-king is totally in brand for Kingmaker. You said no spoilers, so I'll just confirm that the module has several potential plot hooks for the ethically flexible wizard.