This week I bought one MR3020 and flashed it with the technobit firmware (openwrt). Everything worked fine until the switch of the lan interface to dhcp.
The MR3020 started, but no connection was possible. Trying to switch the MR3020 into failsafe mode failed - neither by pressing the WPS button or by change the position of the sidemounted switch. So I bought a
CP2102 and followed this
guide (no additional resistor was needed).
Afterwards the MR3020 worked again, but this morning the usb psu was defect and I had to use one of my phone usb charges. In the end, I am starting to hate the MR3020.

Actually, if you had another router, you can check the DHCP client list or statistic to find the ip address.
For the power supply, i use 5V from same PSU that powered the miner

There is also quite a nice hardware mod - but obviously involves opening up your 3020... There is a position on the PCB labelled up as a resistor (R113) - located next to the micro USB power connector... Solder a link across this and your MR3020 will happily take its 5 volts from the normal USB connector (normally 5v output only) - which is great because the Technobit boards happily supply 5v down the USB connection (or from USB hub)... Thus effectively powering the 3020 from the supply feeding your miners whilst cutting out the need to run an extra cable just to power the 3020.