If it's actually carrera marble and not "tile" (there IS a difference), then you might well seal the marble after installation but before grouting. Be careful NOT to allow the sealer to drip down into the grout joints.....this might prevent a good bond for the grout. Aside that, you should be "good to go."

Have you read up on using epoxy grouts with marble tile? Every epoxy grout I've looked at says specifically (sometimes in the finest print) to NOT use it with natural stone.

You may end up with 'picture framing' where the edges of the tile darken permanently.

From Laticrete's website:

Certain types of stone (e.g. Thasos White marble, White Carrara marb/e, other statuary marbles, and other absorptive stone) may draw the grout liquids into them causing a "picture framing" effect which will darken or discolor the stone. Coduct a test area to determine suitability and acceptability.

Here is a link that might be useful: LATICRETE