ANSWER:

It’s more rewarding to pray longer surahs. You can pray as many rakahs as you wish. 

The sunnah is to pray 8 rakahs in units of 2, followed by 3 rakahs of witr and its best to pray longer surahs even if you have to hold the Qur’an or phone in your hand if you don’t know those surahs. 

Is it better to offer less rakats with longer surahs or more rakats with shorter surahs when praying taraweeh?

Taraweeh, Tahajjud and Qiyam-ul-Layl |