That sounds crazy enough to be something I would design

That bug in the pictures is really cool. It looks to me like you'll have no problem building something capable and fun [sm=thumbs_up.gif]

I'd like to comment on a couple of your points:

I think the tubing size will depend upon the overall size of your design. Do you have a scale in mind? A wheelbase length? What do you expect the longest section to be? If there are enough supports, you could probably get away with using smaller diameter tubing (or rod) and rely on gusseting to lend strength. As for the turning radius, if it will be 4ws you may not have a problem needing much wheel cut. My truck has only about 26 degrees on each axle at full lock, but the overall turning circle is manageable because both axles are steering.