I was reading this: Explanation of what an OP_RETURN transaction looks like and I wondered if the second output "value" : 0.00200000, was at all necessary. Can I just have a OP_RETURN with a 0 output in the transaction?
If you want to retain any change, yes you will need two outputs to return unspent Bitcoin to yourself. If you are spending for example a 0.0001 BTC output, 0.0001 to fees, then a single 0 BTC
OP_RETURN output would be valid.