The only time I use Windows on my computer is when I have data on it that I need. I used to mount my NTFS partition on my linux table but I stopped doing that since I never used it.
So the only time I use Windows is if I am at work, school, or need files from the NTFS partition.
About Autocad... there are many alternatives. LinuxCad is a free one, there is also qcad. There are some commercial ones such as VeriCAD, Cycas, and IntelliCAD.