You can setup as many router in your house as you want. I have like 3 setup at my house mainly due to all the devices we have.
First Router is in the first floor living room, with the Modem. This provides the wireless to most of our devices, but it has a few devices hardwire, like our TV and other streaming devices. Speed goes up to 90Mbps (my internet is suppose to be 75Mbps, but not complaining)
Second Router is in my room on the second floor, connected through ethernet to the first floor Router. Connected to my computer and all my gaming consoles. Speed are also good, goes up to about 90Mbps as well.
Third Router is in the second floor "game room", this one is actually connected to the router in my Room through a Powerline Adapter and provides wireless to 2nd floor. Connected to more consoles, TV and streaming devices. Speed is a little slower due to powerline adapter, but get around 60Mbps which is still very good. I would have like to hardwire it, but too far from my room.
Originally the Second Router was just a Ethernet switch, but recently the switch was causing disconnects (might be because it was trying to get internet from first router and the powerline adapter). Switched it out for a Router with a WAN port so it will always get internet from my first router and its working fine right now.