Does that mean, you have not tried so far if OTG works for you? At least with my firmware (G800FXXU1ANJ2) it did not work - but it is possible (but unlikely) that official firmwares exist that already support OTG. Maybe you can test if OTG works and post your firmware version here.
My smartphone is rooted but it should also work without root. You have to flash a new kernel (contained in a boot.img file) with Odin. Although this does not root your device it will probably trigger the KNOX counter and void your warranty. As only the kernel is replaced, the Android system and your data will survive - so you don't have to start again. But I would recommend to safe your data before, just in case flashing the kernel fails.
Thanks so much for your help