Yup, you'll need those steel idlers. Also, you won't need first gear anymore, so you might want to either lock it in second gear, or get the single speed conversion which also locks it in second and removes some weight. Even without second gear, you'll have wheelie popping torque
and high speed.
I imagine you are using a receiver pack for the servos and Rx? If so, you might want to pick up a UBEC (sold here). It is small and lightweight and lets you do away with a receiver pack (and the weight associated with it). It will take power from your main batteries and digitally convert it to 6v @ 3A for your receiver and servos.
If you are using 14 cells, want tons of torque and speed, and want to stay a little cheaper on the brushless motor, I'd say a BK Wanderer 7XL motor. If money is no object, those Lehners are great and a bit more efficient. I don't personally have experience with them, but someone else should be able to tell you what will be equivalent.
The tough part might be the 30 minute runtime. Brushless is more efficient, but it still needs some juice. If you are just bashing, you might be able to get 20-30 minutes if you use some of the higher capacity (4200mAh) batteries. Racing is more demanding so runtime will be lower if that's what you are planning.
To get an idea of the speed you'll have, try
this. Your actual speed will probably be a couple mph better than what it says, but it'll give you an idea anyway.