So currently im squeezing 95 watts on my zotac 1060 mini. So I reckon 500 watt should be pushing it but obviously you can expand more cards at a later stage getting a bigger psu.
So if your board only accepts 4 cards, then you can get those PCI-E extenders which extends your PCI-E cards from 1 port to 4 ports XD.
I want to try one of those things at a later stage instead of having to buy new PSU ect...