Customising the Sultan RS?

Dear CTzens. I am once again turning to you with a GTA Online question. After reading the comments on my last question (what car to buy) I have decided that the Sultan RS would be the best choice. And, with a budget of 1.8 mil. , I also thought that it will be acomplishable. So, having converted mine to RS, I have about 1 million left, and am thinking how to spend it. Should I keep it plain and tuner: