does anyone know how much space it has and how many Sp it costs?

AFAIK, it's a weapons refit of the Avenger class (or possibly the Exorcist). The main difference is that one weapons slot per broadside carries macrobatteries, one carries launch bays and one carries lances.

FFG hasn't published anything to date, at least not that I've seen.

In the old Battlefleet Gothic rules, the Retaliator is a Chaos Grand Cruiser. You could probably model it as an Exorcist; the BFG statlines for the Retaliator and Exorcist are identical except for the weapons. The Exorcist has 2 launch bays and a double set of macrobatteries each side, while the Retaliator has 2 launch bays, 2 lances, and a single set of macrobatteries each side. FFG seems to like dedicated carriers, so I'd suggest using the Exorcist as a template.

Cheers,

- V.

It's in BFK, p. 106. What you seek is a Chaos vessel, heretic…

I don't think they'd like me to type it up here, but you can find it, the fourth Chaos vessel in Battlefleet Koronus.