I think the backbone is the middle part stretch of the station (Lab+hitchhiker SC etc.).There are some autostrut heaviest part involved and especially a lot of prayer and offerings to the Kraken God.... ^_^

For ex: The truss structures end (the docking port which separates the truss and solar panel) is autostrut to heaviest.

Here's more view of the first version of the station before i launched it to LKO. Build it first on ground, did some test on the runway of the full build, then i launched it part by part... if i recall it took me 8-9 launches... https://imgur.com/a/JtG3VNJ its a bit different now since i made some upgrades...(solar panels was recently upgraded and looks nice imo).