Yes, you will have to turn the Smart off.
As far as the number of channels goes, there are only really 1, 6 and 11 at 2.4GHz because the channels are so close together, they interfere with each other. An oversight in the original design. Only 1, 6 and 11 are far enough apart to be completely separate.
At 5GHz they are already set four channels apart but the airwaves are crowded and your Wi-Fi is not the only thing out there. Channels above 48 can be used but they may clash with things like radar and so are obliged to use DFS (Dynamic Frequency Selection) and jump to another channel if they detect a radar signal etc. This means 36, 40, 44 and 48 tend to be the most stable for home use.
