Folks, soon I will possess an S5. I am now looking to buy a PSU.

At some point in the future, it may be anywhere from 2-10 months, I will probably get another miner such as S7 etc.

Couple of questions -
1) Should I get a PSU that will support future miners? Ie. get something like a 1300-1500W PSU?
2) If yes, surely this will be overkill for a single S5 and will end up costing me more in electricity bills?
3) Should I instead get something like a 750W PSU and then later in the year buy another PSU if/when I need one?

Appreciate any thoughts.