It says With all cs files installed this will work with minimal configuration And a lot is preset up like the conversations files and example cars NOT: nothing is pre setup even though it says it is.
All Chat Commands are listed on the page with example take the time to re read it...
chassis size is done by how many modules you add to the config for the vehicles. the modules are item shortnames witch can be obtained here https://www.corrosionhour.com/rust-item-list/ the will be placed from frount to back on how you have the the list