The link below has all the details of tahajjud.
A few points:
– You don't have to pray all 11 if it's difficult. You can recite the last three
– In salatul witr which is the last 1 rakat namaz, in qunoot you can recite any dua you wish and it's not necessary to follow the same sequence of duas given. You can even ask for what you wish in your own language
– Tahajjud can be recited any time between Isha and fajr although the closer to fajr, the better.