For the first problem, you should check whether your devices support 5GHz. You can have a google.
If any one of your device supports 5Ghz, but it can't see the 5Ghz network, change the 5GHz channel of the router to 36 or 144. Other channels are worth testing as well.

For the second problem, you might choose a wrong firmware. Check the hardware version first and choose the first firmware for the right hardware version.
The firmware should be extracted to a bin file.