1- This is the proper Seegha for Nadr. One would say “Lillahi Alayya…” and then states what they want to do. So this is a correct Seegha according to all scholars.
2- Since he did not fulfill this Nadhr, he has to pay a Kaffara, which is feeding ten poor people. The minimum for each poor person is 750 grams of food (such as wheat, rice or dates).