2000 Volts above me says some very true things. Please, listen to what he says.
As for your list and making it competitive...you don't need to spam anything. I don't spam anything in my army; I've got a bit of everything in there, but I've been working on my list, and fine-tuning and tweaking it for almost a year now, and I've yet to discover someone who can thrash me. Picking a "theme" is not the same as making a spam army.
As for you, if you have a single battlewagon, here's my advice:
Make a foot slogging list. You need to decide if you're going to make a shooty list or an assaulty list from there. Something invaluable in a foot-slogging list is Gretchin. A solid wall of 29 gretchin+2 runtherders spread across your front advancing in front of your army means that your boyz on foot will all have 4+ cover saves marching up the board.
If you're going to make an assault army, I'd get stormboyz in there. You're short on models for a foot-slogging list, and I don't know exactly what you have to work with, but I'm going to take a few guesses to try putting together a sample army list for you. A note on nobs: They should be in a vehicle or not in your army...you've got that part of it right. Nobs in a foot-slogging list are just wrong. Unless they're nob bikers. Is your competition coming up going to allow you to proxy stuff? Something to find out. In the meantime, try this:
Do you have trukks? Any? If not, you can proxy your battlewagon for a trukk. Put your warboss and the nobs inside of it. If you really want, leave it as a battlewagon and put your nobs and warboss in it. Your 2nd
HQ should be a mek with a
KFF if you're going to run mechanized (so that your vehicles get 4+ cover saves from the force field). For a foot-slogging army....the Big mek is a waste. Why spend 100 points on a mek with a
KFF to get a 5+ cover save to anyone within 6" when you can spend 107 points on gretchin to pretty much give 4+ cover saves to your whole army?
Presuming you're going foot-slogging and taking the mek with the
KFF out, I'd replace him with a weirdboy. Stick Old Zogwort in there if you can afford him. I *really* like Ghazghkull Thraka, I pretty much always take him instead of a warboss. On the turn he waaaughs! he grants you an auto-six for your shooting phase movement (running) for your whole army and makes your whole army fearless. He himself gets a 2+ invulnerable save for that turn and the following opponent turn.
Having him also pretty much means that you don't need to take bosspoles on your nobs, because your boyz are going to be fearless when it counts....which means you won't be rolling leadership.
Next, your boy mobs disturb me. If you're going to make a shooting list, it should be centered around squads of Lootas. They pour fire downrange and your boyz mobs offer supporting fire, but aren't really trying to cross the board. If you're making an assault-based army, then big shootas don't belong in your boyz mobs because you're going to be running during your shooting phase.
As for your nobs, you should individually equip each of them to make 10 different wound groups. Additionally, you should have a painboy in there to give them all feel no pain. Don't worry about cybork body; once you learn how to play with them, you won't ever really need invulnerable saves, and that 5+ doesn't hit enough to justify spending the points to get it. Here's my favorite 10 nob configuration (with 'Eavy Armor):
1. Painboy (Grot orderly)
2. Bosspole
3. Waaaugh! Banner
4. Powerklaw
5. Powerklaw + Ammo Runt
6. Powerklaw + Kombi-Skorcha
7. Big Choppa
8. Big Choppa + Ammo Runt
9. Big Choppa + Kombi-Skorcha
10. Normal Nob
All of those nobs are two wound, WS5, 4+ armor save, 4+ Feel no pain. They're in a trukk or a battlewagon, so you don't need to worry about them being shot at until they assault unless your vehicle gets shot out from under you. If it does get shot out, its either destroyed or exploded.
Destroyed: You disembark in such a way that the vehicle gives cover to more than half of your unit from anything that can shoot at you, meaning you have a 4+ cover save.
Exploded: The vehicle makes wreckage and a crater, which grants a 4+ cover save to your nobs.
No matter how you look at it, your nobs always have a 4+.
As for assaults, you don't need that 5+, because a smart nob squad isn't going to suicide themselves into a
MC or a squad of terminators with lightning claws, or an incubi squad or something. That's what Ghazghkull on the Waaaugh! with his 2+ invulnerable save is for, and you use the nobs to counter-assault (or to go hit something easier).
Your deffkoptas are two wound models. They can do the same wound allocation magic that nobs can. They can outflank and they're an integral part of your anti-tank (since you don't have tankbustas) so they should ALL have twin-linked rokkits. On top of that, give one a big bomb, and if you have points, give one a buzzsaw. Otherwise, at least take twin-linked rokkits on all of them.
If you want reliable heavy support for a ground-pounding army, take a squad of killa-kans instead of those big gunz. For weaponry, take grotzookas. You've then got 3 assault2 STR6 blast templates on a walker squad, and they're STR10 dreadnought
CC weapons, which can rip apart any vehicle. You do need some sort of anti-tank capability, and I think you'd be well served with some.
There's a lot more to say but I've already said a lot, so I'll say this instead: If you like any of these changes, or ones that have been made in posts previous to my own, then edit your original post to reflect the changes that you agree with. If you can't do some, or don't understand others, feel free to post that too. Once you have a revised army list, then we can go through a second round of critiques.
Orks can do all the things that all the other armies do better than all the other armies can, 
bleeeeh 2/0/2 but what fun they are when they win 
loot loot loota!!! 
Orks (5,000 pt Apoc Kan Wall, 1850 Bikerz)
Grey Knights (1850 Crowe Purifiers, 2500 'Ard Boyz Draigo)
Sisters of Battle (Seraphim spam)
2400 Empire
3000 Tomb Kings