What's the main difference and improvements between different hardware version (v1 vs v1.6 vs v2 vs v2.2 vs v2.6) of tp link omada er605 (tl-r605) vpn load balancing router?

I know difference between v1 and v2 is that v1 have up to 4 wan support but v2 have only upto 3 wan support and additionally it has one usb 3g/4g modem support.

So is there any more difference between these different hardware versions ?

I also want to know that in v2 can we plug different adapters in its usb port like

1- usb to lan adapter

2- Wifi usb adapter

3- usb mobile tethering 

4- wireless wifi hotspot via usb