HI mate. I’d say, regarding the DVD’s, I don’t think you can play them in the dvd format on your tab and would need converting to a video format that is compatible with your device first, then transfer them. If you have a PC, you could use a PC programme called Handbrake for ripping and converting and it’s free… If you google ‘using handbrake to rip dvd’, can give you some pointers on that.
If your tab doesn’t have inbuilt wifi, then a dongle would be the way I would go (again, as long as it’s a dongle that’s compatible with your tab).
On the dash cam issue, afraid I can’t help but I’m also interested in this myself so will be looking about the net and here for info.
cheers