+1 for the current kit balls, perfect for the job and will last very well if built and broken in nicely before the car is run.
When it comes to replacement time I'd say either stick with the Kyosho balls or if you fancy ceramic try the RudeBits ones or Kyosho's own.
I've not tried the RudeBits tungsten carbide ones yet so can't comment on those other than to say they are high spec.
If you need any Kyosho info please ask but as Kev says both cars go straight from box to track with just a front spring change to Orange. From there it's all down to personal preference on the setups and I'm sure you'll get plenty of help if you need it
