Concerning your question regarding qiyammul layl and tahajjud. Qiyammul layl means to stand at night (in prayer), while tahajjud is to pray (at night) ofter one sleeps after 'Ishaa, but before Fajr. So tahajjud is considered a form of Qiyammul layl. This type of Qiyammul layl is preferred. But if one fears that he/she won't be able to wake up before Fajr to pray tahajjud, it is recommended that they pray it (Qiyammul layl/Witr) after 'Ishaa before they go to sleep.