I think the premise that there might be an obscure company leasing dark fibers to people is hopelessly optimistic.
But, the question about utility poles should be answerable at the township; they should know and have records who has been granted use of the rights-of-way along their public highways.
Yes, with VLANs and managed switches. But if you don't already have managed switches, you'd have to replace both of them. By far the cheapest solution is to put a small wired router (e.g. I've owned a TPLINK ER605 that would work, performing routing and DHCP) between the ONT and SW1, and then reconfigure the WiFi-Router to turn off the router and DHCP functions, leaving the internal switch functional and allowing the WiFi to serve as an Access Point.
Ethernet if you can.
Wired ethernet is better than MoCA. MoCA is better than any wireless solution. A commercial access point wired to the router could rival MoCA. Mesh with wired backhaul is the best among mesh solutions. Mesh with dedicated frequency backhaul is better than other mesh. Mesh is better than any extender. Extenders vary from not good to snake oil to not good snake oil.
Flash technology used in SSDs has a limited lifetime in terms of writes per location. Although SSDs have the intrinsic feature of wear leveling to attempt to spread out those writes across all locations in the device, eventually one or more locations will wear out and no longer accept data.
As there is no easy way to determine how many write cycles have occurred in an SSD prior to purchase, there is always a risk of getting a device that starts failing the day after one installs it.
90 degree pass? I wouldn't worry about it.
Whether attaching an Ethernet cable to the unused Ethernet jack on the mesh unit would work, depends on the particular model of mesh unit and what the jack is used for. If the jack is labeled WAN or MODEM, it won't work to connect to your computer or console... but it is very unlikely to break anything. Even if something goes haywire, just unplug your cable, temporarily unplug power to the mesh unit, and then plug power back in to the mesh unit should restore everything.
If the jack is labeled LAN or SWITCH, then it should work for a wired connection to your computer or console.
The T7 series gets very hot under sustained writes, hot enough to be uncomfortable to hold, and as you've found, sometimes hot enough to shut itself down. I have also seen that problem with intermittent writes if the drive is buried under papers, so I make sure that it is on the desk with available airflow near it.
If I'm going to be doing a bulk write to fill up one of my non-Shield T7s, I literally place a metal bowl with ice directly on top of it for the duration of the transfer. But I've found that extreme step is only necessary when I'm writing continuously. YMMV.
I found my R8000 to be very reliable for eight-plus years. Although I've replaced it with an OPNsense router so I can have VLAN and multiple WAN support, I still roll it out once a year to support my Twinkly holiday lights. Sorry yours had an issue.