Rooting the phone simply gives root access...it doesnt change your software. Personally, I havent bothered rooting my phone for a few models now because I simply havent needed it for anything.
A reset wont take long, but I would be presuming that you will end up with a "fresh marshmellow".
You would need to flash your phone with the correct Aus version of Kitkat to get back to where you were. I have used Odin before flashing phones with no probs, this video might help
Always make sure you are using the correct version of software for your phone.
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