1. Based on your use case and rural location, you should use 80 MHz channels. Your repeaters will thank you! 2. Meraki's Auto-algorithm is good, but in your case, I recommend trying to manually adjust the 5 GHz channels, ONLY on your gateways. Remember there are only a handful of non-overlapping channels (36+, 52+, 100+, 166+, 132+, 149+, and 165) available in the 5 GHz band when using 80MHz wide channels. So start with those channels, and then re-use channels only on access points far away from each other.
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