Welcome Slyrman. First off, nothing wrong with small games. 400-500 point Combat Patrol games (
http://www.adepticon.org/wpfiles/2017/201740Kcp.pdf) are a lot of fun.
Right now, I would suggest buying absolutely nothing until 8th edition comes out in ~3 weeks.
For the time being, the general thinking is that right now, the chosen from the
DV box and the Warp Talons are pretty terrible (or at least over-costed). I don't have points in front of me, but here's how I would put your list together.
Combined Arms Detachment (Maybe Word Bearers ?)
Dark Apostle (using the chosen with the Power Maul)
20 close combats weapons + pistol + 2 flamers
All with Mark of Khorne
3 Chaos terminators w/ combi melta + power fists or chain fists.
1 Land Raider
Put the possessed, and chaos lord in the
LR on turn 1. I like Mark of Khorne on mine so that the possessed get 4 attacks each on the charge.
Run the Warp Talons as raptors with maybe 2 plasmas guns or multi-meltas.
Stick the sorcerer with either the 10
CSM or the remaining cultists (with autoguns). Up to you on how you want to use him. Since it sounds like you don't have any daemon models, summoning (or anything in malefic daemonology) is right out. I would probably go level 2 (unmarked) on Telepathy (fishing for invisibility) or Geomortis.
Tactics depends a lot on how you want to run your army. Nothing, outside of your Warp Talons, are very fast, and you don't have a lot of long range shooting. Probably want to hang out at mid-table and charge in with the Dark Apostle + cultists + drive up the land raider and charge straight into assault with the possessed and the Chaos Lord. Have sorcerer + culists or
CSM, camp on objectives and let the sorcerer do his thing. Deep strike in the 3 terminators behind some really hard target and take it out with combi-melta and clean up with the power weapons.