October is a great time to start generally. So far, we are having a pretty good winter, which helps the spring NOBO hikers and also fills reservoirs and regenerates springs. But for the SOBO fall hikers, a good summer monsoon season is what really helps. So - stay tuned. Pretty much figure on carrying 3 liters. Of course, a lot depends on how many miles you can cover in a day - more miles = getting to more water sources each day. Also depends on how much food you're re-hydrating, your personal conditioning, temps, etc. You're from the cold, so nights at the northern end probably will seem balmy to you! Ha! But you shouldn't hit anything below the 40s at night generally. The desert areas will be great that time of year. Maybe a tad warm for you during the day = more water, sun umbrella, more breaks, but nights will stay in the 50s. Have you also joined up on the FB Arizona Trail Class of 2019? Good resource. Most of our rain is over by Sept., both around Flag and here in the Valley. But last October was WET. So, as we all know, Mother Nature can do as she pleases!