The sand is a very finely graded sand. It is high quality. Bill V. has used it on marble I believe without problems.

No need to seal the epoxy grout.

Is your tile crackled? I read on Phylhl's kitchen reveal a post by the tile manufacturer who posted on her site, that the crackle may need to be sealed to prevent stains from getting into the crackled areas. With stone, you seal first avoiding the grout spaces, then grout. It helps the grout release from the tile I believe. You might want to seal if your ceramic is crackled. I am just guessing that this would be done, so I would consult the Laticrete tech department. You don't want the sealer to get into the grout spaces.

On the laticrete site somewhere I thought I read that for 1/16" grout spaces you could leave a smidgen of the powder out to make a slightly wetter mix.

When I grouted my floor I did it myself. But when I grouted my walls I had my DH follow behind to cram the falling grout into the spaces as I missed them. We worked about 3 feet apart. First me trying to grout the walls with the float, then he followed picking up the pieces.

My bathroom project was the 2nd and 3rd grout jobs I have done, and I'm a girl ;)
... But I had help.