Vegas Effect - When I changde the blend mode to transparent, the whole image disappears.

Just fix this by changing Image Contour: Channel to Alpha for anyone's reference

When you set the blend mode in any effect that generates pixels to Transparent, the only thing left on the layer are the pixels created by the effect. 

You need two copies of the Logo. Add vegas to the top copy, adjust to get the look you want, and animate the parameters to get the edge behavior you want. Now set the blend mode to transparent, set the opacity of the bottom copy of the Logo to 0%, then move down the timeline to where you want the logo revealed, and set the opacity to 100%, so the logo fades in. Now set Opacity keyframes for the Top copy of the effect to achieve the reveal you want to get.

Another option is to add Vegas, set the blend mode to Transparent, add a full frame mask, enable the mask in Compositing options, then animate the opacity of the mask. Something like this:

No idea, honestly. However, since you are zoomed out to 25% despite the resolution set to full theres always the chance that the default thin line simply gets gobbled up by the on-screen sampling or some hardware acceleration limitation. so at the very least zoom to 100% and switch to software-only rendering.

Mylenium