What additional devices would I need to ensure that all 3 stories in my home are covered?

You would need at least 1 dual-band, gigabit capable WIFI router.  For your home we recommend a system similar to the Google Wifi Mesh Router.  Its 'puck' system design creates a “mesh” network, and is ideal for multi-story buildings.  We sell the Google Wifi for $99 per puck, or you can purchase multi-packs from Best Buy, Amazon, Costco, et cetera.