To start with;
those wheels are a big no-go.
They are way too large!
I am using 1/10th wheels and they are big allready. you need to think of the drivetrain.
the wriath 7k motor seems to make the little bugger fly. (and is MORE than enough motor for it) I am using a mamba 8k on it, on 6 cells gp1100's it'r pretty fast allready.
A must have hopup is the gearbox, sold on ebay for about 25 bucks.
If you get the hitec servo you need to overcome the saver problem. I made my own horn for it to work.
My advice is to get the team kit, and watch what dies first. (it's a pretty tough drivetrain, except for the output cups on the diffs)
here is a short movie of my rc18 with the 8k on only 6 cells.