Perfect LTE & Wi-Fi network 2020?

Dear community.

Primary goal: to achieve almost the maximum download speed of the internet tariff for all devices in the whole house (two floors) on every device (2-3 laptops, 4-5 smartphones, 1 smart TV) throughout the day and even while on the move. The LTE Internet tariff currently delivers "up to" 50 Mbit / s, which is usually achieved directly on the LTE router. Possibly. Will the LTE tariff be extended to 80 or 150 Mbit / s.

Desired goal: The hardware for the network should cost a maximum of 300 euro and be bought (advantage: no connection to the Internet provider).

According to my current research, in theory this should be achievable with the following hardware configuration:

LTE router with at least LTE standard Cat 6 (with carrier aggregation in LTE bands 20, 3, 7)
Either integrated in the aforementioned device or connected as a separate device with a network cable: WLAN router (or access point) dual band (2.4 + 5 GHz) + 4x4 MU-MIMO + mesh compatible with repeater
Wi-Fi repeater with dual band (2.4 + 5Ghz) + 4x4 MU-MIMO + mesh compatible with Wi-Fi router (AP)

Is there currently a manufacturer that offers exactly (no more and no less) what is needed for this? It is a great challenge to keep track of the many devices from different manufacturers.

I have something like this.

I have a FRITZ! Box 7590 as a router in the office (1st floor) - one line goes into my server cabinet with my 48-slot switch and from that into two 24-slot hubs to which the installation cables to the individual boxes on the other floors and go to the garden

on the ground floor (living room) there's a FRITZ! Box 7490 as a wlan access point.

in the garden I also have a LAN line on which a 7390 hangs as an AP. During the renovation at the time, I installed 750m cat 7 pipes.

This means that we have a maximum download speed of 49 Mbit over Wi-Fi with a 50 Mbit DSL line in the whole house from the basement to the roof and in the garden

With the 300 euro budget it could be tight, but you should get two Fritz boxes, a hub, a switch and a few meters of cable plus the necessary sockets for 450-500 euro