For that setup you need at least a 1300 watt Gold or Platinum rated PSU  and I would add to that it should be a good brand like Evga or Corsair.I think since you will use an LHR unlock miner and get near 57-59 Mhsh with such card that will throw in more power usage so to be safe use a minimum a 1300 watt PSU like those I said.I would even go ahead and buy the 1500 watt version just to be 100% safe as one such card consumes near 200 watt each with the LHR unlock.

Many says that a closed case is better for Gddr6x memory which they tend to overheat the temperature memory quite quickly but even open air rig is OK as long as you provide to the cards very good additional cooling,these type of memory the Gddr6x really needs it badly otherwise it will start to throttle and give you a lower hash rate.