I have found myself with a fairly decent starting Nighthaunt Army and now I'm asking advice from any Nighthaunt experienced player on good option for Units / Heroes to build upm to 2,000 (+).

I have a double set of the Nighthaunt minatures from the Soul Wars box sets (2x Shroud Knights on steeds, 2x Soul Guardians, 2x Spirit Torments, 2x Lord Executioners, 8x Grimghast Reapers, 10x Glaivewraith Stalkers and 40x Chainrasps).