how do i can get the sd card to work

this camera supports micro SD card,max 128G,the first time you use the micro sd card in this camera, you need take the micro SD card to format,

how long is the usb charging cable, and can it be powered on 24/7?

Hello nick hallowell, Greeting from FREDI, this camera can be powered on 24/7,Please rest assured that the use of.

Does it support external network? In order to be able to watch it from my mobile or pc connected from a diff network?

yes,it does,your phone can see the video when the phone connected to difference network,and you can see the video through computer,and it just support IOS system or Android system computer.thank you for your question.

Do you have to be connected to wifi when using remotely?

Yes it has to be connected to wifi .