Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh

Praying during the late hours of the night is one of the greatest supererogatory acts of worship; as such it merits tremendous blessings and spiritual rewards.

So, you are to be commended for doing so.

Tahajjud, however, is praying after waking up from sleep; it is still more rewarding as it takes the effort to wake up and pray. Having said this, I must also point out, if you think you may not be able to wake up you still will be rewarded for praying. Allah is Merciful, and He does take into account our weaknesses and circumstances.

As for witr, you don’t need to repeat witr if you have performed it after Isha. We read in a report, “There is no need to pray witr twice during a single night.”

If you are planning to pray Qiyam (supererogatory prayer during the late hours of the night), then you might as well postpone witr till the end.

Almighty Allah knows best.