Generally speaking, it's unnecessary to have a disk to help you install the RE580D. You can have a look at their instruction guide. https://static.tp-link.com/res/down/doc/RE580D(US)_V1_QIG.pdf...

login password for your wireless router? The default one usually is admin. Did you change that? If you changed that, it requires to put the new password. If you forget it, try to hard reset the...

This should be affected by daylight saving time. What's your time zone? try to choose minus one hour standard time as your time zone.

check whether you have configured the range extender successfully. Generally speaking, the galaxy s7 should support wireless roaming.

Is the internet/WAN IP on Archer C5400 the public IP address? Make sure you can ping the port in internal network. better to provide the device's ip address and port number which you want to open.

These smart devices can be controlled through the cloud account. If you do not use cloud account, how can you control it remotely? In other words, it works just like normal switch..