While searching for OpenWRT firmware, I had to look for a US specific one (which had -us in its name) and shorten the filename to firmware.bin before installing.
Setup password-less SSH once: ssh-copy-id [email protected]. (This might not work. If so, directly upload your SSH public key from the UI. Also, remove this instruction!)
Set custom DNS server to that of Next DNS: Network -> Interfaces -> WAN/WAN6 -> Edit -> Advanced Settings -> Use custom DNS servers. Once for IPv4 and IPv6 each.