Hey Cheryl~ As ms.queenbee said, they are like apples and oranges. If it were me, I would do all the SU stuff first, then see where you are at. You can do so much with the SU product line. You will be thrilled with the results you get there.
If you then find you are wanting more...down the line some, then you can invest in some copics. Based on the info you have shared, I would start with the CU/Copic color matches and build from there.
Hope that helps some!