Hi Tom, so you got started, good!
The Miss Geico model will be possible to do on this cat, not that hard, just a lot of work
One thing.....almost afraid to give any comments these days....
Why did you make the inner tunnel stringer same size as the middle stringer? Now you don't have a rim to glue the tunnel to...
As for the weight, don't make it to light, it will just flip a lot.
My cat is 22lbs RTR and runs 94km/h with a very mild tuned zenoah [5+HP], this was not a one time deal, it runs consistent between 91-94km/h.
And as stated by lildude, the steps are on an angle, this makes it easier for air to get through.
One important tip! Keep cg as low as possible! It will corner better.
Marcel