You cannot disable the Intel GPU - if you do, you'll get no display. The AMD GPU is simply a co-processor - ALL video data funnels through the Intel GPU on its way to the screen.
For "2", check with AutoCAD. Their applications tend to require true discrete AMD or nVidia GPUs -- which your system doesn't have. If that, as is likely, is the case -- you'll need a higher-end system to run those applications (or you'll have to live with the performance on the Intel GPU).