I’d contact the local Peplink partner for advice.
In the meantime, as background reading:
- There was a thread in the forum that had a similar (not the same) situation that might be helpful: Typical setup for home office
- There is also a comparison table that could be helpful: Peplink.com - Model Comparison
And a $0.02 worth of personal opinion:
Requirements:
- 1 Gbps router throughput.
- 2 WAN ports, each handling a fiber-enabled connection.
- 1 LTE connection as backup in case the two wired WANs fail.
Musings:
There seem to be two viable (and not-too-expensive) options.
- Balance 20x + a USB ethernet dongle
It provides the LTE modem and one wired WAN
Its throughput is 900Mbps (close to 1Gbps)
You get the second wired WAN connection by adding a USB-Ethernet dongle.
Question-mark: How fast the USB-ethernet connection can go.
I have no real experience with that, beyond occasionally employing a USB-Ethernet dongle on a Balance 380 HW6. That connection (across a 1Gbps fiber) achieved only 335Mbps, where the Ethernet WANs to the same fiber achieved 900+ Mbps. - Balance Two + a USB modem dongle
It provides two full-speed wired WAN ports
Its throughput is 1Gbps
You get the LTE fallback using the USB-connected modem
FWIW: The set-up for a home office for one of our people predates the Two and the 20x, and required more than two SpeedFusion connections (it serves as a hub for remote locations of various kinds). She ended up with a Balance 380 (for the two separate ISP WANs - we’re quite risk adverse 
) and a MAX BR1 Mini LTE-A connected to the third WAN (could equally well have been connected by means of the USB-Ethernet port) as the cellular fallback.
If we were to do it again today I’d expect her to select the Balance Two (as per the above) with a SpeedFusion upgrade license to handle more than 2 peers, and the USB-ethernet dongle connecting to the BR1 (or a USB-modem dongle, if she did not already have a BR1 at hand).
In any case - contact your Peplink partner.
Cheers,
Z