My internet setup is as follows:

Internet > wireless > 4G router > wireless > Main Router > PC (wired) and other devices (wireless)

As you can see the Main Router (which I connect all of my devices to, because it's faster in terms of internal network speeds and has a longer WI-FI range) connects to the 4G router (which is the access point to the Internet) wirelessly.

I want both routers to be wired. However, the 4G router has only a single Micro USB port which also acts as a power supply and the Main Router has no USB ports.

So what sort of (Micro) USB to Ethernet adapter should I buy (suggestions from experience welcome)?

Is it possible to transfer power from the Main Router through its Ethernet port?

If I use an adapter with a separate power supply, will it supply the 4G router through the Micro USB port?

Models:
Main Router: Tenda W308R
4G Router: Is an Infomark Biscuit Mini provided and customized by my ISP.