You can find you're latest firmware on sammobile.com
I would suggest you go back to stock now, and don't flash another custom ROM until you are willing to read about it first... And I mean, like read about what AOSP is, what the features of different versions are, and then read and understand everything there is in the thread about the ROM you want to flash. Sorry for being a little harsh, but if you had done those things, I doubt you would have chosen to flash this ROM.
But since you didn't do those things, here's the answers to your inquiry.
This ROM is out of date, and no longer being maintained. I assume that you actually meant multi-window, not multitasking. This ROM does multitask, but multi-window is not supported in this version of AOSP.