You can create only one additional partition that will be on the HDD, not the SSD and it will not be part of the Fusion Drive:
https://support.apple.com/en-us/HT202574
If you choose either Linux or Windows, my advice is to install the OS in EFI mode and not BIOS emulation mode. Also, if this is done correctly, you won't need to use rEFInd or rEFIt as a boot manager. The mac's built-in boot picker can be invoked via the option key to choose which OS you wish to boot from.
Here's a video I made a while back showing my old Macbook Pro dual booting Ubuntu and OS X in pure EFI mode:
[video=youtube;w0RM3L8r4cE]https://www.youtube.com/watch?v=w0RM3L8r4cE[/video]