Spoke Size / Spoke Length Database - What size spokes do I need?

It will make a difference, but it isn't clear whether Corima have already allowed for this in their stated ERD. Probably not, judging by the small difference between internal diameter and ERD. You also need specific concealed nipples, don't try to build it with conventional ones upside down as the slot head on a conventional nipple will auger through the carbon and wreck your rims. Corima sell a pack of 5 CX-Ray spokes with nipples for Eur.9.50 in a 268mm length, or 5 CX spokes with nipples for Eur.6.90 in a 271mm length. One of these is likely to be the best fit for your build.

I forgot to thank you after reading this earlier, mdcc, so: thanks for the help!
I've just send Corima an email to see what they have to say.