Update guys: I managed to make it work, no problems.
I used the first partition as SWAP, it turns out that the partition was there because it was holding a bootloader for Windows 7, as the drive used to boot 7 before I moved it to the SSD.
The Windows 10 installation is actually legacy, so I went to the BIOS and changed settings to force all boots to be in legacy, to prevent any ugly mishaps.
Thank you all for your help!