Well way back when I wanted to start using those guys I made sure to bring up the fact that if anyone wanted to care about spoilers they should let me know but everyone was fine with it, this however was something I am desperately trying not to spoil myself and if that means stopping what I'm doing then you can bet that's exactly what I'm going to do. (There's a reason I fight so hard against this on BL in the first place.)
It is still a Type-Moon forum after all.
The information I've given is much less of a spoiler when compared to giving unknown Servants' Identities and explaining plot details.
Caster's past and identity has been explored in F/E to the fullest, so whatever there is in CCC, it isn't exactly 'accurate' to call them spoilers of plot, but rather, they're little tidbits of here and there - like cherries topping the cake mostly focusing on character development.
Most important of all, the huge bulk of the info comes from F/E. The CCC part isn't that much of a spoiler but rather re-affirmation of something that had been stated in F/E already. You already know about the fact that Casko is an aspect of a Divine Spirit.
If you absolutely want to skip whatever info I'm posting though, then feel free to do so -- but remember that my character in herself has nothing to do with CCC.