Having a white car myself, and a daily at that, I'll add two things to the spot-on comments above...
Clay is probably needed (you can do the baggie test to make sure), but be aware it may cause some marring of the paint that a polisher would be recommended to remove. On a white car, probably not as noticeable, but be aware it could happen.
You could stop at HGG and likely be just as happy with the results. In my experience wax doesn't tend to add much to the shine on a white car above what HGG will, and HGG should last longer than the BW for protection.