Something to think about is that the MCP23017 is not the most straightforward device to use for someone new to Arduino. Firstly, it's quite a complex device with a lot of options. Also, It really needs clean power, and bypass capacitors are an absolute must, and they must be as close to the power pins as possible. I'd go for at least 10uF in parallel with 0.1uF. Whichever design you use, make sure the reset pin is in a known state.
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