Like all the other comments, I would have to say add some more tactical squads and a devastator squad or two if you can.
I have a fairly large DA army that's nearly 8000 points. For the greenwing part of it. I have 3-10 men tactical squads that I can break down to 6-5 men units. I also have 22 veterans I can mix in to give me more tac squads if need be. As far as Devastators go, I have 2-5 men squads right now with 4 lascannons in one and 4 missile launchers in the other. I'm debating if I want to build another one but mix up the weapons and make sure at least 1 or 2 of the weapons is the Grav cannon. I already have Heavy Bolter's and Plasma Cannons mixed in as part of my veteran squads. So the Grav Cannon is the only heavy weapon I don't field at the moment.
As long as the Devastator Squad can be protected they are a nasty long range threat to my opponent. I myself prefer to run the lascannon squad since that's their strongest weapon. But when I played in apocalypse games I have both dev. squads in my force.
Another cheap troop choice is to get a scout team and equip it with sniper rifles and put it in terrain. For about 80-90 points you get some 4-36" range attackers using sniper rifles and your sgt is using a 48" range missile launcher.
The rest of my greenwing army includes a command squad, 2-5 men assault squads, 2-5 men scout squads, 3 predators, 3 rhinos, 3 dreadnoughts, razorback, drop pod, land raider and the DV leadership characters: Company Master Balthasar, Librarian Turmiel, I-C Seraphicus.
As far as expanding the rest of the chapter. From looking at what you have, I would seriously consider getting either Sammael's jetbike or buy a generic landspeeder along with the DA upgrade pack. It allows you to change a normal land speeder tornado is Sammael's with twin assault cannons and twin heavy bolters. You also get his 14 front and side defense on either model. Having it join your Ravenwing and maybe a landspeeder typhoon with its 48" range would give you some very strong support for you bikers.
My RW consists or a 5 bike command squad, 2-6 bike squads, 6 bike black knight squad, 3 assault bikes, LS Tornado, LS Typhoon, Sam's LS, Sam's jetbike, Dark Talon and I have both a I-C and a Lib. on RW bikes. I like it when I have ran a mixed RW/DW army so having a strong presence of both has been good to me in the past.
For a Deathwing addition, get another terminator squad and make it all close combat with TH/SS's. Maybe getting Beliel and run him as the model shows are run him with a TH/SS and attach him to the unit. If you also have the funds consider getting a land raider crusader and run it forward full of DW and have them assault out of it.
My DW consists of a knight squad, command squad, 4 DW squads, Venerable Dreadnought, Beliel, land raider crusader and both a I-C and Lib in termie armor.
Otherwise look for a cheap Azrael and Ezekiel to get. Azrael is points expensive but is a beast to take down and Ezekiel is your level 3 psyker. A couple of very good choices for your HQ choice. These two and Sammael are probably the best three HQ choices right now for DA. I also have Asmodai, but I prefer a standard I-C over him.