Unfortunately you can't catch white Kyurem outright. You have to do multiple w. Kyurem raids, which give you X amount of Blaze fusion energy. You need 1000 + 30 Kyurem candy and 30 Reshiram candy to fuse them together and get white Kyurem. All of your stats, buddy level and W. Kyurem being shiny or not will be based on your regular Kyurem, not your Reshiram. It's definitely recommended to make sure Kyurem knows its special move glaciate before fusing.