Hello,
The first Deco BE25 must be physically connected to the ISP router, using an RJ45 cable.
Subsequent units connect to the first unit via the BE25 network (very easy to configure using a mobile phone).
Best regards
To increase the Wi-Fi range, a single Deco BE25 is sufficient as a mesh router if you connect it to your internet provider's router via cable or Wi-Fi - a connection via NFC is not technically intended and not possible as the Deco BE25 does not have an NFC function. For even better coverage, especially in larger flats or houses, you can add additional Deco units via Mesh, which then automatically network with each other. Two routers are therefore not absolutely necessary, but can be expanded if required.
I was able to do a search and according to the manufacturer's instructions there is no built-in ceiling or wall mount. Yes, it can also be connected via Ethernet including daisy chain.
To connect your Internet network to Deco, you can use one of the RJ-45 ports available. These ports are self-sensing, which means it doesn't matter which one you choose to connect your modem to. Deco can function as an access point or router, depending on the configuration you choose. For best results, make sure your modem is connected to one of Deco's RJ-45 ports, then configure the system using the TP-Link Deco application.