I just completed 2 bathtub surrounds, all glass. Use what the tile manufacturer recommends for thinset. The tile I used came with a white backing. If your tile is unbacked, you're supposed to knock down the ridges after spreading the thinset so the grooves don't show through the tile.
The Redgard should not show through the thinset. If your tile requires modified, don't use Kerdi. Kerdi wants unmodified. There are arguments that modified can be used with Kerdi, but I wasn't going to risk it as the tile is too expensive to replace.
I waited 3 days to grout... just to give the thinset time to fully dry and let any moisture out. I don't know if it was necessary but did it anyway since glass isn't porous.