Purism certainly looks like a good idea and their specs looks adequate for software development and multi-tasking.

Have you seen Qubes OS? I think a combination of that and Purism would be a great step towards vastly improved security and privacy. If you need Windows you can run it in a secured virtual machine in Qubes OS when you need it. Same with any Linux distro or MacOS

More on Qubes OS here: https://steemit.com/qubes-os/@samu-paha/qubes-os-a-reasonably-secure-operating-system