My main point is figuring out where the other end of the line is, at the original ISP, or beyond that. And please forgive my lack of vocabulary, I have limited networks knowledge.
In my experience the way this works is that we buy a leased fiber connection - say 1GBPS, usually terminated either in a regular datacenter or in a business park somewhere. Sometimes you're buying that line from the same entity that is also selling residential Internet access in nearby neighborhoods (IE CenturyLink) but the business group you're dealing with is almost entirely distinct from the residential Internet service group.
1GBPS will go further than you think - you can put 700-800 heavy usage customers (cord cutters, college students, etc) on a 1GBPS link and never (or very rarely) max it out. Selling higher speed plans doesn't really increase the max throughput on the network either, except in fairly predictable 'bands'. That seems unintuitive, but most people don't really increase their Internet usage depending on the speed of the connection (other than at a few thresholds, IE going from <1mbps to something that allows cable-cutting) so selling a faster connection just gets them their data faster and frees up your capacity for the next request.
You would think that at least 50% of people would be watching Netflix at the same time each night, but as of yet that doesn't seem to be the case. (At least not on any of the networks that I've been familiar with, which are in pretty tech-savvy areas like I mentioned, with heavy users.) It also helps that you can get one of Netflix's caching servers (can't remember what they're called) once you hit a certain threshold of traffic to their network.
The key though is that the more customers you aggregate the less traffic you can plan for per customer. So for example if you have 100 customers you might need to budget your network at 4-5mbps/customer to make it through peak times without slowing every one down too bad, while if you have 1000 customer you can get by with ~1.5 mbps per customer.
How many people are you going to service per point of access?
How are you going to deliver connectivity to all your points of access?
1) I've used Cambium and Ubiquiti and several others. Ubiquiti is hard to avoid because it's so damn cheap and it does work reasonably well, although Cambium is noticeably more robust. The latest stuff coming out is fixed 4G LTE, several companies pushing that gear in to the WISP space and I suspect that's where things will start to take off.
2) 30-50 for Cambium and Ubiquiti APs. Fewer if possible. On a large network the APs tend to be the bottle neck.
3) Fiber to primary POPs and then high capacity licensed wireless backhauls 2 to maybe 3 towers deep in the network. Depending on the local weather it's not unrealistic to get a licensed link that can support 800mbps to maybe 1.2 gbps over 3 to maybe 5 miles.