A couple of points that I left out earlier:
You can check out the community-recommended hardware Community-recommended computers for unofficially recommended hardware that multiple people have found to work well.
Also, don’t forget to submit a hardware compatibility list report if you find a computer that works with Qubes OS. It’s easy to do as you can just run ‘qubes-hcl-report’ in dom0 and copy the .yml file to an AppVM with ‘qvm-copy-to-vm [destination VM] [Qubes-HCL-model.yml]’ and attach it to a new topic in the HCL Reports section of the forum. It will help anyone else looking to know how well that computer works with Qubes OS.