Besides just the design of the chassis, the material selection is very important. What works for a race car with a 2 year life is very different than a street car that lasts 10 years and 100,000 miles.
I had it lucky I had my fellow teachers at the college here plus help from a local university for the information I wasn't able to find otherwise(structural engineering and the like). But if you are not going to college or working at one just showing up asking questions will probably not get you much help unless you can get someone there interested in your project. There are enough 'experts' on the internet that I would probably base most of my research on books and very little on web based information if you can't interest an engineer in helping. Some of the frames I have seen people build online are pretty scary.
Also don't ever use chromoly, structural steel is much better for road use, trust me.
Using any tools like Autocad can give you a false sense of security if you don't have experience building things with it. It is one of the more annoying programs to use. I say just jump in and start building. When in doubt run over it with a truck or beat it with a sledge hammer and see what breaks. That usually gives pretty good results. But relying on computer tools to do your testing is nowhere near as good as testing out ideas yourself.