1) Is there a basis in the Sunnah for saying "Wa Iyyak" (and to you too) to someone who says "Jazakallahu Khairan" (may Allah reward you with good)? 2) Is it permissible to say: "Our Great One is the Messenger of Allah, may Allah's prayers and peace be upon him"? And is not greatness an attribute of Allah alone? 3) What is the ruling on saying "by Allah's power" instead of "Insha'Allah" (if Allah wills), believing that nothing happens except by Allah's power? 4) Is it true that welcoming a pilgrim and seeking their prayers is recommended?

There is no origin for the word "wa iyyaka" (and to you too) as a response to supplication, but it is a good word meaning "and to you the like of what you supplicated for me." There is no objection to describing the Messenger of Allah, peace and blessings be upon him, as 'great', for Allah has described him as such. The description of 'great' has also been applied to other things in the Qur'an. There is also no objection to saying "by the power of Allah," meaning "if Allah enables me." It is recommended to escort a pilgrim or traveler, bid them farewell, and ask them for prayers.