Delaying the witr Salaah

Q: My question is about witr Salaah:

1. After performing Esha Sallah at 8.00pm, can I delay my Witr Salaah till 11.00 pm(my sleep time)?

2. Can I combine Tahajjad and witr at the above mentioned time?

3. What will be my last Salaah before I go to sleep, Tahajjad or witr?

Ma'zoor

Q: Almost all the time I get a few urine drops after urination, sometimes I don't get any. I wear an underwear and before every Salah, i wash the place where I think urine drops might have touched, is it ok? Plus some days (not daily) I have gas issues as well. Am I a mazoor? I read quranic wazaif for long hours, if i getup to make fresh wuzu, I probably cant finish the wazaif (for 1 hour or more). I make a wuzu before salaah and continue my salaah and quranic wazaaif.