First, before spending a lot of money on a truck of material, buy six or eight boards and stain and finish them. Modern flat sawn pine is pretty ugly when stained, not the picture that most people think of when they see old pine floors, which were mostly old growth, quarter sawn boards. Unless you are after a rustic look, #2 is going to have too many defects to cut out, resulting in a lot of shorter boards. Also the modern pine is a lot softer than the old longleaf pine and is going to show much more distress from everyday use. There is flooring manufactured from new pine, but I don't think the typical lumber yard stuff is nearly floor quality.