How much white chocolate should I use in a white chocolate cake?

I am trying to develop a white chocolate cake formula. The recipes that we tried were dry or did not have the right flavor or consistency. I found no guide line as to how much white chocolate to use. Can any one help? I am concerned that the white chocolate contains sugar, fat and emulsifiers. What I do not know is what percentage should white chocolate be in this recipe that I created?

Here is what I have so far: I have not tried this recipe yet. All I did was the math!

15 oz. cake flour,
2 oz oil,
4 oz butter,
15 oz. sugar,
7 oz. of eggs,
4 oz. milk (hot to dissolve white chocolate),
1 tablespoon + 1 teaspoon baking powder,
1 teaspoon salt,
1 tablespoon vanilla extract,
4 oz. white chocolate (real chocolate containing cocoa butter),

I plan to use creaming method, pre sifting dry ingredients and adding the white chocolate and hot milk just before adding eggs, and bake at 350F.

Is that a good amount of white chocolate?