Sushi rice should be transparent when cooked?
Many questions here!!!

Sushi is simple but very difficult to do properly.

The rice is not transparent; it is only "shiny" (probably doctored for the picture). (well, maybe it is transparent and I have not seen it! :-) )

When you prepare you rice, do you add sugar and rice vinegar ? this will make the rice sticky and lump together so that the rolls do not crumble away.
When you roll the rolls, do you apply enough pressure to make a solid roll ?
Also, use a sharp and wet/humid knife to cut the rolls and do it in a single stroke (no see-saw movements).

Damp nori gets a little bit sticky; by applying a thin slice of mange or avocado, it should be enough to stick to the nori; also you can use the rolling mat to help "squeeze" the mango or avocado to the nori.