Ok issue 1, importing. I want to answer this question but I do not use Google Sketchup (I'm a Max enthusiast), but as far as I know, the texture you use should be applied and messed with in the modeler and when you export you have to include that image in the export settings.
Next, when you see the bridge instead of your model it means you exported the collision information (rigidbody.x), but not the mass (rigidbody__.x). Those 2 little underscores are so you can tell the 2 files apart. Export your model for both of those. Also, you cannot export anything but a cube or sphere for rigid bodies that have physics.
Finally, this is my favorite because you described 3 different problems in the same sentence and the issues are so vague I'm probably the only person here that would even take the time to TRY and help you, but I'll do what I can.
So, the issue with the wheels sinking into the plane object has happened to me, and my best guess is because of the way the model is made, the polygons are stretched and collision is shaky with car wheels in particular.
1 reason why the car has no traction could be the friction setting on the plane and/or on the car (the grip settings).
As for the camera jumping...geez I'm not even sure what you mean, but in the editor if you zoom out too far the camera goes nuts. Try to keep your world small enough to fit in that range (I don't know what the range is, but I know 1,000km is far beyond it)
One final thing. Every object in rad has settings, and one of the buttons on the settings panel is Help. Click that and you are magically transported to a page that tells you everything you need to know about that object, its settings, and ways you can apply them. I use it often even for objects I know inside and out
