A 550w or better power supply (from a good manufacturer with good reputation) would be enough, but probably best value for the money is at 650w even if it's more than needed...
A gtx1060 consumes up to 125 watts, 2060 super goes up to around 180 watts and 2070 consumes up to 230 watts.
Future video cards will be less power hungry for same performance.
So whatever system you'll make will consume less than 400w which is well within even a good 550w power supply's capabilities.
As for mb, that depends on the budget... z370 based boards would be ideal if you want overclocking and so on but you could probably live just fine with B series chipsets (b360/b365) that aren't as great as z but still good enough.... not that you can OC the 8700 chip anyway.
An alternative would be to sell your 8700 and go with Ryzen and AM4 board, where there's less things to worry about and you have only B450 or x570 chipset boards to choose between and all allow overclocking and have decent features.