You might wanna add 4th like the dividends project. There are several of them these days. I know its still risky that one day the project will collapse all of a sudden. Its kind of a NEO giving away GAS like you said which is hard to trade. EOS projects distributing dividends is distributing EOS tokens which is easy to trade unlike GAS.
Bitfinex was hacked and kind of paid off the debt. So you are very vulnerable to hacking.
@ op by USA tax law mining is not passive income it is active. I do not know any laws in other countries.
It must be active, though as a miner you don't literally do the work but you are still maintaining the hardware and pay for the bills. You will constantly check whether you actually have mined coins.