Brian Blankenship

Can confirm, I love my Ubiquiti network.

There is nothing that says you have to have an accurate listing for your IPs location. There are still wide swaths of the net registered as a small farm in Nebraska (its the dead center of the United States).

Mind the Wire gauge. CAT6 23 AWG might not fit in a CAT5/5e terminator.

I know they have some long range equipment, but I think its all PTP (Point To Point).

Yeah it's possible. But there might be a problem for the client side devices having enough power to talk to the base stations, assuming a few hundred feet between the them. And 5Ghz is basically out for that range. You can do point to point over miles, but a wifi adapter on a laptop doesn't have the output power to reach the far. If these are going to be vehicle attached devices for police cars for example, then you can manage more power. If you are going to be providing this as a paid service then you might need to consider providing hardware to long range TX/RX. https://www.ui.com/products/#airfiber

You can bounce from base station to base station the same as a cell phone does from cell tower to tower. However you need to deal with the range issue. Would this hypothetical Mesh Network be a municipality maintained infrastructure?

Depending on what the Pi-Hole is running on, there is really no need to have a second one. I have a pretty extensive network (36 Clients (Personal Devices and Servers, 10 network devices and far more personal devices during parties and such). I have a single RPi 3B+ running Pi-Hole and it's not even breaking a sweat. Unless you are in a enterprise level environment, I wouldn't bother with 2 of them.

On the back of the modem or on the power supply, it will have a DC Volts call out. That's what you'll want to aim for and exceeding it too much will let the magic smoke out. Sometimes that call out will have a variance such as "+-5%", but if it's intended to be wall powered then I doubt that will be noted. Without knowing the variance though, you are going to need to experiment. You could, if you had another modem of the same type pump up the voltage and let it blow. Then back your voltage down to a safer level for production.

Go for a server. A server that has as many SAS/SATA ports you can get. Max it out with as many SATA SSDs as you can. You not going for capacity of storage, but capacity of access. More devices mean the load gets spread out more. If the clients are all limited to 1gbps then they'll max out at 125MBps. 10 1g clients will saturate 1 10g server port. If you need to do all 60 at one time you'll need at least 6 10g ports and a switch that can handle 60gbps of traffic. You COULD for imaging put a 10g NIC in the client and image at that speed. Then remove the NIC after.

It's not out of the realm of possibility.

My next test would be to connect to a new network. A friends network, a new coffee shop whatever. If it acts the same it might be hardware failure. If it only happens on your network, then it might be a windows registry key or some other OS level thing.

A server is only going to give you so much bandwidth. That's why there are Steam Cache Servers.

The only real reasons to have 2 NICs are to have them connecto to 2 separate networks, or to LAGG them together. You aren't gaining anything by having both of them connected at once.

Your best option: Make very good friends with your nearest neighbor that has access to any kind of a decent ISP. Work out getting a line for you installed there and then use antennas to get it to you. A pair of these https://store.ui.com/collections/operator-airmax-devices/products/powerbeam-m5-620 should get the job down, assuming you have a direct line of sight between them. You very well may need some masts to get the height you need.