If your 110 is US gallons, then a dozen discus would work fine. Your PH is fine for domestic discus, and breeding has nothing to do with PH. Discus eggs don't fertilize well in hard water, it decreases the hatch rate, so it's water hardness and not PH that screws up the hatch. It's advisable that only adult discus be placed in planted tanks anyway unless you have had good success with discus already. Discus will stunt easily because of water quality, and planted tanks are hard to clean. Yes, you can probably get away with 2-50% water changes weekly. You probably won't grow 7" or 8" fish, but average fish of 5" to 6" which is fine. You do not need RO water for any reason unless your faucet puts out liquid rock. Generally, if you can drink the water and live, discus can too.