Usman Asar

Which platform are you looking into for scalability? Linux or Windows?

Youtube doesn't gets buffered fully, its progressive streaming, only those parts are sent that are requested, for that you have to have a streaming server.
which format and container your students are using to upload videos? If you can ask them to encode using H.264 in MP4 container that may solve issue of buffering on localhost.

where is moodle hosted? local?
also the format they choose in original upload have effect on end viewer as browser may be trying to play but get limited by your hardware resources. Have you tried on other PC/Phone?

Wait for sometime Javed, some hosting providers re-calculate space every 12 hours.

you dont have to carry all data at once, skip cache, localcache and temp folders, rest compress folders individually to carry on to new server.

Tom, you have to ADD course summary block.