When you're shooting, you can leave your camera on Auto White Balance, or you can choose one of the WB presets in your camera, or you can do a Custom WB using a grey card. In each case, it may or may not be necessary to make further WB adjustments to your Raw files once you get back to your computer.
I have no opinion about your white balance method - do whatever suits you.
All I wanted to mention is that there is no difference to the quality of your Raw data, no matter which method you choose. Whether you use CWB and get it exactly right, or AWB and get it wildly wrong, and have to correct it later, the end result is exactly the same.
Your camera captures a finite amount of data on its red, green and blue sensors; and that data is set in stone. The white balance setting is merely an additional piece of information which is used to interpret the Raw data.
So choose the white balance method which suits your own workflow, and be happy in the knowledge that you aren't making any difference to the quality of your Raw files.