I am running 5 RX 480 on a windows 7 on a nanopool. A rough calculation is that I make $150 a month from all 5 cards. My investment into it is about $2000 and my ROI is about a year. Are my calculation right??
your calculations are not right!
your ROI is the difference in the price you paid for the hardware & the hardware's resale value!
so if you paid $2000 for your hardware & you can sell them for, idk, $1500, your ROI is $500!
if you have fairly priced electricity you'll most probably roi & will make some profit; don't be much stressed about it!