Make your logo in photshop (or whatever)
Put it on the timeline byitself. Make sure it is on top of all other tracks. Change the size and placement to where you want it. Change the opacity of that layer.
Yes.
Create the logo in whatever tool you prefer, whether it's a 2D or 3D image. Save it with an alpha channel.
In Vegas, use Track motion to put it to the correct size, and place it in a corner.
If the alpha isn't auto sensed by Vegas, then right click the media and choose Properties, then select Media tab, and in the Alpha channel dropdown, choose Straight.