What type of parts are you trying ot make? 2-D or 3-D. If you intend on making 3-D parts Solidworks is by far the best CAD program on the market. Once oyu build the part you can set loads on it and see where the weak spots are. You can then put all the pieces together and see if there is any interference. If you build aero parts you can perform a flow analysis on the part to see if it is "clean" in the air. They can be imported into mastercam, Qmax (waterjet). You can also build parts to be made out of a sheet (like
oil pans)