@Praetor: First you need to fix your list. You can only take 2
HQ, so drop the Librarian. Other then that here are my suggestions for your slots and what you should do with them:
HQ: I would say ditch the Chapter Master and Honor Guard as well. Take a captain and a command squad instead, trust me, you will love the
FNP that the apothecary gives you. The second
HQ should be a chaplain, either with a jump pack, or take Cassius. He is well worth the points and will just eat up Orks, and will survive much better. If you decide to take Cassius throw him in with the Sternguard squad I suggest, or Vanguard. Either way he will help. If you just take a regular Chaplain then give him a
JP and throw him in with your Assault Marines.
Elites: You should put in another Dreadnought, drop the Terminators and put in Sternguard in a Razorback. That will help you to lock up some more Orks and give you some added firepower for a very reasonable point value. Both of your dreadnoughts should be taking heavy flamers and
TL Auto Cannons. They will whittle da boyz down nice and easy.
Troops: Give your Tactical Squads a flamer and
HB each, and with the points you save from the reduced
HQ cost you should buy another one and have 3
SM squads of 10. Throw them all in Rhinos, and just camp them along the back. You can fire your
HB every turn and the rhinos give you great survivability, especially against orks. Do your scouts all have sniper rifles? If not you should give them all rifles and throw Telion in there too. Use them to pick of Ork vehicles and Nobz, they will help plenty. And not to mention, if Telion hits his target, YOU, not the other player, YOU get to decide who gets them. He is great for getting rid of that annoying Nob with a
PK and a Bosspole.
Fast Attack: Love, love, love the assault marines. Be sure to give them two flamers, and give your sergeant a combi-flamer and Power weapon. They will just chew through boyz with those two templates and all of those attacks. If you have the extra points you can throw in a 5 man Vanguard Squad for 125 pts, and they are a good stop gap and cleanup crew, especially with a chaplain attached.
Heavy Support: I love the Vindicator, and it has saved my butt plenty of times, but I don't really take them against Orks. It is really overkill, and you can spend the points more wisely. I say take either 3 Whirlwinds, they will kill boyz just fine, and they are cheaper, or take 3 Thunderfire cannons. When you start throwing out 12 templates a turn, you will see boyz just start to fall in stacks. You might even make your opponent cry.
I hope that helps. That list will help you plenty, and you will kill more boyz then you can imagine.
PM me if you have any more questions.