This will sound harsh, but have you taken any courses in FEM- Finite Element Method (that is what this stress analysis is called)?
The problem with FEM is that you always get a result, but the result is only as good as the assumptions and limitations of the model, and the expertise of the designer in supplying the mesh and boundary conditions. SISO!
If you don't have to engineering background to understand the assumptions made in the software and limations of it, and to set boundary conditions and mesh, you will end up with, at best, pretty colored pictures of distorted parts, and at worst dangerous parts waiting to fail in service.
I would suggest you best bang for your buck would be to enroll in some FEM class at a local engineering university.
Once you have the knowledge to use the various packages on the market, you will also know what you need.
For modelling parts, Rhino is very popular and has a reputation for being easy to learn.
There is some info on FEM here: