I think the issue is that you are asking for a mile or more of range and that seriously limits the options here. You will need a radio service that has that sort of capability. Assuming you're looking at using this unlicensed, that rules out many options open to licensed business users or licensed radio amateurs which could easily reach a mile.
FRS or ...
It seems that you only found setups, using routing. But it is no problem to setup the WiFi access point on the RasPi to be on the same internal subnet as the internet router. You have to bridge the wired connection to the router on eth0 with the wlan0 interface of the access point. This way you are even on the same broadcast domain as the router, so your ...
Create a new file called wpa_supplicant.conf on the boot directory containing the following text:
Do not use notepad if editing the file on a windows PC. Use something like Notepad++.