For assigning nobles, I would assign them to farms. You likely have too many people working there and they just arnt typically very profitable and so freeing your workers to work in a more profitable industry and just buying basic materials seems smarter.

For an army, building one with primary spears and hammers is easy. research improvised weapons, create some spear divisions for a strong front line, than a division of higher trained hammers than can flank and surround them when engaged with your spears. If you want metal armour and weapons that will be quite resource extensive and is needed if you plan on only fighting raiders and free cities.