Is it permissible to combine the intention of worldly benefit with the intention of righteous deeds, such as fasting and prayer, and does this include seeking knowledge with the intention of reward and out of a love for learning?

The intentions accompanying the intention of drawing near to Allah do not affect the validity of the deed nor nullify its reward, although the most complete state is for the deed to be purely for the sake of Allah the Almighty and seeking His pleasure, without any consideration for one's own desires.