Sorceror Mark of Nurgle, Nurgle's rot, plasma pistol
8 possessed marines Mark of Tzeentch
8 Thousand sons with sorceror doombolt
6 Chaos space marines melta
997 what do you think?
Ok.. Right Your missing 500pts, which I would use for Rhinos myself and some heavy support and a Icon on the CSM squad.
The Possessed, 30+ points per model.. and for a special rule that you will not get to use 2 in 6 times if you run them with the Sorceror... Not that fantastic, but puting an IC in the squad does deal with the lack of frag grenades which makes them almost useable.... I would look and swaping them for more berserkers, or even terminators.