Aahz
Don't get confused with Steves tank and the others , Steves is one of the few tanks that use a motor that does not come with a integral gearbox hence he needs that large reduction ratio.
The advice is good on the site which is why I and building a test chassis out of cheap wood , to see where all the parts/holes need to be.
The wheels drive etc will be for the real tank , and when the test chassis can drive it's self then it will be copied to provide the real one.
regards paul