That is up to you.
I use 4 of them it has taken alot of messing around but saved me alot of money compared to nvidia.
When mined only for ethereum you can underclock/volt your gpus to use much less power.
My rig is also used for gaming but even then I only use 500w of power with 4 rx580 8g.
The choice is yours save money = more hassle, more money = not always more hassle.