Replacing whole egg beating process by separated egg white and yolk beating in a recipe which calls for the former?

the answer to both your questions will be yes. the cake flour will give you a lighter cake due to the lower protein content (less gluten=lighter and fluffier cake). separating the egg withes from the yolks in this recipe is not really necessary because you have already a good amount of rising agent in the recipe itself but is you wanna make the entra step fold the wipped egg whites at the end, they should lightened the texture even more.