Hi All, I am trying to build and future proof as much as possible, an LTE solution. I have bought a Sierra Wireless EM7565 and a USB modem, with the original idea of using it in my TP-Link C5400 router with the USB modem… I have found The firmware on the TP-Link does not allow, and there is no open source, I should have researched more…mybad 
… So I am rethinking a solution… It may actually work out better, but want to ask if my design idea is possible…I already have an extra 250gb Msata Samsung SSD…and I have a Netgear 10gbe switch with SFP… On the Omnia, I would remove the 2.4 module , (and let my TP-Link be the primary router. for 2.4 and 5.0.)… I would add the Msata. Install the EM7565, Use the SFP connection to my 10gbe switch, and set up the Turris as a repeater just for the 5ghz band. (from the TP-Link.) … sounds like it should work, the only thing I am not sure of, is if the Omnia can be setup as a repeater, and still function as a LTE modem, AND have 250 GB storage for a DVR setup. Any advice is appreciated
Perhaps with the mwan3 package it could work, though it currently suffers from issues.
Though not exactly the same but a bit similar concept in packages/net/travelmate/files at master · openwrt/packages · GitHub
A logical combination of AP+STA mode on one physical radio allows most of OpenWrt supported router devices to connect to a wireless hotspot/station (STA) and provide a wireless access point (AP) from that hotspot at the same time.
But that is on the wlan iface and not wlan + lte. Android phones providing a hotspot turn off WLAN.
So it seems like 50/50 chance, trial and error.
As for the internal router space - 1 slot for ssd, 1 for lte and 1 for 5G, remove 2.4g, and/or ssd/lte via external USB.
Question is does the TP-Link router support a multi-WAN-Setup and VLANs (default Internet + LTE Internet coming from Omnia via Ethernet)
On the Omnia it should be possible to configure two Interfaces: LAN Interface bridged to WLAN (you called it „Repeater“, but if your Omnia is connected to your network via ethernet you can configure it as a WLAN-AccessPoint) and a second LTE-Interface for LTE-WAN-access. Those two interfaces should then have two VLANs so they can communicate with your Switch and TP-Link. Routing must be set up correctly on your TP-Link and VLAN-switching must be set up correctly on your switch.
I don‘t know if your LTE-Modem is supported by Turris Omnia
Thanks for the quick reply…after thinking about it , I actually have cat6e cable between the 2 points where I need signal, So I was thinking access point ,but said repeater., sorry for the confusion… Perhaps this will make things easier. Worse case is, I make this Omnia my primary router and use the TP-Link as an access point. I just want to keep the TP Link in the mix, because I “know” it is rock solid when it come to getting signal to a repeater (yes , repeater, ) that is in my separated garage. I do not know yet if the Omnia would be able to do it alone and cover the whole house with wireless. Thanks again.
Using Turris Omnia as your router should make your life much easier I guess 
. Good luck!