Sweet, thank you! I have no CAD experience so I'm definitely expecting a learning curve
If you have strong Illustrator skills, mainly in vector manipulation/boolean...pathfinder type stuff, you should be pretty good. I am of the opinion that graphics people should learn cad and drafters should learn Illustrator. When I got into this in the late 90's I saw there was always a graphics to cad disconnect among professionals.
I vowed to learn both. Illustrator was mainly through projects and tutorials, for the cad I took a 40 hour basic cad class at a tech school. Fell in love with it, and haven't looked back.
The accuracy and scale with cad is what hooked me. I already had quite a bit of Illustrator skill, but I needed instruction to bridge the gap. Picked it up nearly right away.
You can do a lot of the same stuff...it's just how you get there. Cad can let you be super efficient with it's tools. I've found even when I take on a graphic layout project, I use a lot of the tools in cad first...to get at the maths. Then Illustrator to put the lipstick on. The cool thing about 3d is, once you learn one flavor, you can do pretty much all of the same functions across the board.
I've used Cinema4D also. It's more of a mesh modeler, which won't serve you well for what you are doing.
Other mesh modelers are 3d Studio Max and Maya. These are for modeling and animation, and wont have the tools you need to build real world stuff.
Stick to a cad based 3d software. I've used Autocadd/Vectorworks and now Rhino. Rhino is my favorite by far!