In a true parametric modeling application you have a design tree, model tree, browser, or modeling history (different terms, same meaning). This tree keeps a running progression of all actions performed. If you create a sketch of a circle on the XY plane, then extrude that circle to a cylinder, you will show the sketch and the extrusion as the order of operations. If you alter the sketch the model will update.
In AutoCAD you certainly follow steps to create your model but the steps are not recorded in a progression so you cannot simply make a change in the tree and see the end result updated.
I have taught both AutoCAD and Inventor for several years and I believe that it is an equal task to learn each fully and effectively. There are some similarities in construction techniques but the environments are far different.
I am still not 100% clear on your goals. The first and last project you proposed are extremely different and would require vastly different approaches. I think you would do well to focus on learning one of the applications that you feel suits your needs best and study well before confining your thoughts to any specific project.
If 3D solid modeling is your true goal then Inventor may be your better choice.
Cheers,
Blaine
Blaine Young
Senior Engineering Technician, US Army
