If there is no error message during upgrade, it should have been upgraded successfully. After upgrade, did you check if the problem has been fixed or not?

So you cannot find the default Wi-Fi password, right? Your M5360 is V1, right? In this case, you can upgrade the firmware here and it won't ask for Wi-Fi password when you connect Wi-Fi after...

What kinds of difference do you want to know? W8960N is using different chipset as W8961N and W8961ND.

Did you try to connect 3PCs directly to LAN ports of TD-W8951ND bypassing the mini router? What's the IP address of mini router? Did you configure it to make it work with W8951ND and how? The RJ45...

TD-W9970 supports G.inp & G.vector indeed.

You'd better use USB dongle in the compatibility list. http://www.tp-link.com/en/support/3g-comp-list/?model=TD-W8968&location=1151