That would be your decision, you can add additional access points if you like.
You may find a single AC-Lite is sufficient, you may not. It'll depend on the size of the property, building materials and so on.
Sorry I understand that I can have more than one AP but i was under the impression that the router would cover the wireless downstairs and the AP would cover upstairs.you can have as many AC-Lite's or other model UAP's as you like.
Is one AP going to be enough to cover the entire house? Is it an upgrade on my current Superhub 3 or will I need to get another AP and have one per floor?