On a 4MB flash model there isn't space to add LuCI later. So the most direct thing to do is install the 17.01.4 sysupgrade stable release build. Release builds include the web interface. The development builds do not. Always use a sysupgrade bin file when already running OpenWrt or LEDE. The factory files are only used to flash out of TP-Link stock firmware.
If router is connected to the internet you can upgrade directly from the command line.
cd /tmp
wget http://downloads.lede-project.org/releases/17.01.4/targets/ar71xx/generic/lede-17.01.4-ar71xx-generic-tl-mr3020-v1-squashfs-sysupgrade.bin
sysupgrade lede-17.01.4-ar71xx-generic-tl-mr3020-v1-squashfs-sysupgrade.bin
Note that when you copy the URL from the LEDE download site, you must change it from https to http. The wget included with a basic build cannot handle https.
(Last edited by mk24 on 26 Nov 2017, 15:28)