Yes, it matters. USB 3.0 is new and 10x faster technology compared to USB 2.0

It really depends on charger and USB cable

Just reset it and set new password

What device do you have? It may need too much power or it can very well be USB problem

You can access admin area login page or credentials are wrong?You should look at router's back, there you can find information about admin area address and credentials, it may be tplinklogin.com

While they usually do same job SFTP & FTP(S) are quite different technologies, so if the router supports FTP, most likely it will not support SFTP too.