Yes, you can install Windows safely alongside Ubuntu without interfering with the existing setup.
Yes, you can install Windows safely alongside Ubuntu without interfering with the existing setup.
Your Windows 10 setup on the SSD and Ubuntu on the hard drive are separate partitions. A fresh installation won’t impact the Ubuntu partition unless there’s a conflict during setup.
in theory no, but there is a chance that Windows will overwrite Ubuntu's boot loader. to avoid this unplug the drive on which Ubuntu is installed.
It's also likely Ubuntu installed its bootloader on the SSD, meaning you'll need Super Grub Disk or something similar to access Ubuntu and rebuild grub.