Are you combining all documents into a single PDF file? You can only upload a single document per section and any additional uploads will replace the previous upload.
You pay your $40USD with perfect notes, you get the visa, never ever heard of any bus or ticket required at Nong Khai during entry, ever. They also want a passport sized photo
the Vancouver consulate is very responsive, contact them and ask what they require or visit their website and search for the length they want for DTV. Where are you?
since you are on the initial visa you don't have to leave once your work permit is cancelled. As mentioned you can stay as long as the entry stamp grants you.