Is this a necron Dec detachment ( the harvests?) with a CAD? I don't have the book and am going on snipets, but if it is a Dec you'd need a 'core' unit?
Otherwise it looks interesting :) speed for maelstrom, tarpits for tying down hammer units, fire power to deal with both heavy and light infantry, and the ability to 'make' new units (if spiders still can).
Would be a cool theme on the table.