LibreCMC on router

I have finally got hands on a Netgear WNDR3800 router on which I intend to install LibreCMC.

Does anyone here have experience of doing that (or similar)?

I have found the image on: https://librecmc.org/librecmc/downloads/snapshots/v1.4.2/ar71xx/generic/

And there is a sort of instruction here: https://wiki.openwrt.org/toh/netgear/wndr3800#oem_easy_installation

I just don't feel confident about the approach. Is it correct that it might be as easy as just log in to the router and do a firmware upgrade from the administration menu?

At the moment I am struggling to establish connection between the router and my computer. That should be possible even the router is not connected to the internet/modem, right?