The only advice I can give is more for general play, not nessisarily geared towards Daemon players.
Control two or three phases of the game.
For movement, focus on getting flanks and rear charges, maintain 2-1 charge ratio (two of your units for every one of his). He doesn't have any serious shooting except for the horrors so you won't have to worry about war machine hunting but taking a unit of terradons would be good because you can run behind him and march block as well as force flee reactions through your unit (instant death)
For magic I don't think I really need to elaborate on this. Slann + EotG should do the trick. I'd probably not go with 2 Engins though or a second lvl 2 priest. For your Lore I would choose Fire.
Shooting is fairly streight forward too. Taking a Salamander to force those low leadership checks would work wonders. A couple of Razordons works well at mowing down swaths of enemy and Skinks would do awesome at taking down those high toughness models too. Skinks are also cheap so, therefor, expendable.
Combat. Let's face it, no one excells more than Saurus w/ spears. You can bait him into a charge and then counter charge with a couple of big blocks. Also ancient stegs w/ a War Spear (from Skink Chief) work amazingly well and have more of that shooting I was talking about. CoC is also good at getting on his flanks.
I know it's pretty general, but I hope it helps. Good Luck!
