Minimum miles for TWA Elites is 1000 "actual" miles. Elite 1 bonus mileage is 50%, and FC bonus is 50%. I haven't had to fly in paid FC for a long time, due to the free upgrades, but the I believe those miles are applied to the minimum as well. So, for a flight like STL-ORD, it would be 1000 "actual" miles towards status, 500 bonus miles for Elite 1, and 500 bonus miles for FC, plus "Fare Reward" miles for your FC fare, so probably close to 2500 miles per segment.