Welcome aboard. I guess you were looking at Thiers-Issard blades. AFIK they're still carbon steel blades. The silver part could be just from the finish they put on them or other alloying elements (most likely not silver lol).
6/8 is a good size for starting because it's the cutoff mark between small blades and large monstrosities. Even a 4/8 blade will give you a clean shave, so what really matters is what you're most comfortable with maneuvering around your face.
If there is a difference between carbon and stainless steels, it isn't very pronounced. I've had stainless blades that honed up easily and carbon blades that took me forever to hone.