Admittedly, casting Genesis to add space is a significant way off for a starting civilization (they could use Stone Shaped tunnels earlier on), but for the food situation, it just takes one level 5 Artificer/Cleric/Archivist/Healer to make an at-will Create Food & Water item/trap, which can then supply food for 15 * 600 * 24 = 216,000 people per day. So you don't need that many crafters to support a very large population, and level 5 is very achievable using the CR < 1 creature XP farming methods outlined previously.