@kushyoman,

A few things:

1 - We normally recommend placing a mesh node on each of the floors of your home, as the floors of your home do have a dramatic impact on the performance of your network.

2 - For Mesh Networks, you will only be able to take advantage of the roaming features when using multiple nodes; if you are considering a single router/node - I would recommend looking towards the Archer BE800 or BE900.

3 - Your environment plays a large factor in what signals you can get and where, such as if your signal is passing through appliances, or multiple walls. 

4 - If you were to only use one router or node, you would be better off with it being on the first floor due to the fact that routers and nodes create a less powerful signal below the node.

Your coverage would also change depending on which frequency you are looking at (2.4GHZ, 5GHz, 6GHz), Your whole home would likely be covered with the 2.4GHz connection, but you would likely not be able to take advantage of the 5 or 6GHz networks while you are far away from the router.

  @kushyoman,

It would likely be more than enough to cover your home, especially if you are making do with one mesh node right now. You may consider trying to measure your signal on the higher frequencies as they do not travel as far as the 2.4 network, and this is likely where you would see a dramatic change in performance.

The signal coverage is honestly completely dependent on the antennae layout inside the nodes. For Decos, we have the recommendation that one is placed on each floor due to how much less the vertical coverage is compared to the horizontal overall. For routers the recommendation is to place it on the "same horizontal plane as the equipment you plan on using." Check this FAQ: How to place your wireless router for optimal reception and performance

Either way, you will have to pass the signal through the thicker boards and joists. Realistically, you would need to experiment with what works best on the higher frequencies in your environment, as 2.4 coverage will likely have minimal problems reaching between floors- at least compared th 5GHz and 6GHz