Would like to redo my WordPress theme entirely without any interruptions to my production site. Can I upload a new theme into a staging area then move it to production? Typically, I know the production and staging use the same them then update are pushed to the production site. Has anyone ever had a new site in there staging are then migrated to production after it was completed?
Yes, you can upload a new theme and integrate that into your staging site to push to live/production. That is one of the primary uses for staging!
Just keep in mind that if you change the live/production site in any way after the staging site is created that you have to make those changes manually into the staging site as well. Otherwise when you push to live/production any new changes on the live/production site will be overwritten.