The three most important things in a Ork Army is;
The Warboss and his Retinue, all in Mega Armour, loaded in the back of a truck (This works wonders against SM, Necrons etc. I wiped out three SM squads in one battle with these guys for the loss of no one)
Dreads & Killa Kans (My heavy support includeds 2 Dreads & a Battlewagon)
The boys, the more the merry (My army consists of 20 Shoota Boyz, 11 Burnaz, 10 Tankbustas, 15 Ard' Boyz, 10 Flash Gitz (All Have Nobs etc))
Stormboyz aren't the greatest Elite, I much prefer Ard' Boyz, 12pts, 4+ Sv, 3 Assualt Weapons, they tend to surivive being blasted at by SM bolters.
When comes to fast attack see what your army is lacking and fill the gap in. In my case I can kill the enemy in a fuisilade of gun fire, but I lack a little in assualt based Boyz, so Trukk Boyz would be a good choice.
In your case Fire Power in the form of Wartrakks and Buggies or Warbikes.
If I were you I would turn one of your Slugga mobz into a Shootas mob. When comes too their weapons make sure there all the same.
Also you can easily convert normal boyz to Tankbustas, all you need is man hole sizes discs and some skill (This is how I made most of them)
On the assualt weapon front convert, convert, convert, they look a hell of lot better when everything is different.
Oh yeah have you chosen a Clan to base your army around or are you going Freebooter. (In my case I'm Bad Moon, that explains my use of All mega Armoured Retinue and the Flash Gitz) You sound like a bit of a Goff if you go in that direct be carefull when sellecting your army, and use Ghazgkulls (not sure about spelling) profile and rules as a base for your army.