@Kidd 

Your main Deco needs to be connected to the source of internet service, typically a modem but could also be a ONT or a Gateway.  Speeds will be dependent on service, coverage, signal stregnth and backhaul being used.  With Mesh the idea that the main unit must be centerally located isn't as important.  With Deco All units will make a connection with each other and the shortest path for the data to transmit will be chosen by the router.  You said 8 units so I assume that this is a apartment enivorment.  If that is the case i would point out the inherenet security risk that it would create.  Every unit would be on the same wifi and the same network and would be open to each other.  Security wise that is not an ideal situation for tenants or you as the landlord.