Is it permissible to supplicate with, "O Allah, make Satan despair of me as You made him despair of Your mercy, and make Satan lose hope in me as You made him lose hope in Your pardon"? And will a person be rewarded for his struggle against the many whispers (waswasa) he is exposed to?

It is best for a Muslim to ask his Lord to protect him from Satan. There is no objection to asking Him for this, and a Muslim is rewarded if he perseveres and seeks recompense from Allah for any trial according to Islamic law. Allah says: "And We will surely test you with something of fear and hunger and a loss of wealth and lives and fruits, but give good tidings to the patient, who, when disaster strikes them, say, 'Indeed we belong to Allah, and indeed to Him we will return.' Those are the ones upon whom are blessings from their Lord and mercy. And it is those who are the [rightly] guided."