One router should be enough. Ideally you want all of your devices like printers and file shares on one internal network and that's what a router creates.

WiFi connectivity is about radio range and penetration. Stone, concrete and plaster are harder for the signal to travel through than drywall. With that in mind you want WiFi repeaters and/or access points that can serve shadows and dead spots. Repeaters should have good line of sight between them. Access points need Ethernet.

I don't like the idea of proprietary mesh products so have a main router and an access point. This works well enough but requires reconnect if you roam.

I'd be interested to hear of recommendations for an open source mesh because the roaming/reconnect is a nice-to-solve.