1- A CL9 isn't the world's end, but if you want the best performance on games an applications the CL9 isn't recommended.
That Corsair RAM is very good, but take a look of this Mushkin 1600 CL6
, cost $20 more but have a better CL.
2- Yeah, you can install the 9GB in the configuration that you want. So, 2 kits of 4GB for a 8GB total, plus 1GB. You won't have a problem, but the 1GB stick only can run in single channel and this would affect the performance of the other RAM and the rig.
That's why usually the RAM is installed in kits of 2GB(2x1GB), 4GB(2x2GB or 4x1GB) or 8GB(2x4GB or 4x2GB) in dual-channel or in kits of 3GB(3x1GB), 6GB(3x2GB), 12GB(6x2GB or 3x4GB ) etc... in tri-channel (for Intel i7-9xx series)