Upgrade the latest firmware. If it won't work, try to change some wireless settings. #5 and #7 mentioned what you can try...

You'd better test to see if to disable 5GHz helps or not... You can try different channels like 1 6 or 11 and you can also try channel width 20MHz. If none of above settings work, you may need a...

According to its specifiations, cannot. http://www.tp-link.com/en/products/details/cat-9_Archer-C8.html#specifications Support Samba(Storage)/FTP Server/Media Server/Printer Server

You have to open ports for the IP address of the PC which needs to be waken up. Some users provide some configuration suggestions here....

Try universal repeater instead of repeater.

If everything works fine, no need to change any settings... If you don't use 5GHz band, you may disable it. But 2.4GHz Wi-Fi and 5GHz Wi-Fi should not affect each other...