Nest Wifi Pro should be the superior option, but I'm very happy with my Nest Wifi router only wireless mesh network too. Specifications on the various models:
More important is where you place the units. The main/master/primary should be placed centrally, rather than on an outer edge. This diagram tries to show why:
One unit have a suprisingly good range, so one Nest Wifi Pro or Nest Wifi router unit on the middle floor might be sufficient, depending on your layout, material in walls and floors. Start with fewer rather than many, buy one more if you need it.
Here are some more guides on placement and how to find the right amount of units:
