I want to dual-boot with Windows 10 and thats why I'm going to install the os to a secondary drive. What partition should I create besides / and /home? I currently use legacy mode in the bios.
For legacy BIOS mode, the very first partition should be a 1 MiB Reserved BIOS boot area. You have a couple of considerations regarding other partitions. If you want to encrypt your root filesystem, you need a separate, unencrypted /boot partition. If you want hibernation, also known as suspend-to-disk, then I recommend a swap partition with at least as much disk space as RAM. I also recommend that this be encrypted, but that gets a bit more complicated.