Multiple Windows options in Grub Menu

I'm getting 2 Windows boot options: "on dev/sda1" and "on dev/sda2". What does this mean?

Don't worry, what you observe is normal and common. These 2 Windows entries in the GRUB menu both boot Windows the same way. I can tell you how to remove/hide one entry if you indicate the URL provided by Boot-Repair.

What implications does this have for my continued Windows usage and for when I may remove the Ubuntu installation later?

No bad implication. You can use Windows normally whatever the Windows entry you choose. And you can uninstall Ubuntu in 1 click via OS-Uninstaller.