1) WiFi Range is not that great for the device, also it heats up a lot. so not advisable to run off wifi hotspot from the device itself.
2) If you can connect any 3G/4G dongle on the device then you should be able to use USB teathering, I'm using without any firmware modification on my ASUS AC66U
3) Its not 100% reliable and there are fluctuations during bad weather, but still decent enough to replace bsnl.
4) I had earlier used the phone as wifi hotspot and connected my router in repeater mode but it has few disconnecction issues so decided to go for a dedicated wifi hotspot instead, but as reliacne locked the sim with handset I was no longer able to use the hotspot and had to switch back to handset, I tried setting up usb teathering and was successful and have been using like that since.