I looked into this a while back, ‘what is your threat model’ and ‘why are you installing Qubes’ are going to be important considerations here
Duel-booting Qubes is very much not recommended, as any program inside the secondary OS (Windows, in your case) gets greater access to the dom0 disk space than should be permitted under the Qubes threat model. The duel-boot setup effectively undermines the security model that makes Qubes worthwhile to use. Here and here are some pretty relevant threads
It’d be much better to back up your windows data, install Qubes over the entire disk, and set up a windows Qube under the hypervisor’s supervision