Default Help with getting Kitkat

I found a SlimRoms Kitkat rom called Slimkat and I downloaded it along with the very large gapps it suggested I get. They suggest I wipe everything and install via TWRP. Can I dual boot it with my stock from a second rom slot so I don't have to wipe? So I would make a rom slot, install the OS from the the .zip from within TWRP, and then reboot right? How do I get the gapps on afterwards? I am very inexperienced when it comes to installing roms and TWRP.

Thanks,
Robbie Rioja

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