Hello, in the paper handling settings you can set the trays to plain 8 1/2 x 11(tray 2), and 8 1/2 x 14(tray 3). As for the other question if you go into the configure device menu, system setup, tray behavior, then select use requested tray. Now the only way this can work is if both trays have 8 1/2 x 11, for it to switch to another tray after it is out. Also, you can set the default paper size in configure device, printing, to letter, and if 81/2 x 11 is loaded in tray 2, then it will print from there.
Hope this helps....