Cannot.

Your hardware version is V5? If so, to upgrade the firmwrae, you have to download the latest version for V5. V6 is a different hardware version and corresponding firmwares cannot be accepted by V5.

Did you extract the file first? Did you upgrade the firmware by cable connection? If possible, try different web browsers and PCs.

If you restart it, you can login, right? Did you try "On its web interface, go to Access Management---UPnP, choose Deactivated and Save."?

WN723N v3 has no soft AP feature but many other adapters can do that. I am using TL-WN822N V3. How does soft ap work? Read this. http://www.tp-link.com/en/article/?faqid=767 You have to ensure that...

As I know, WN822N V2 and V3 support Windows 8 but I am not sure if Windows 8.1 is supported as well. http://www.tp-link.com/common/Promo/en/win8compatibility/