My 1st Job help and advice much appreciated bizzaza mosaic tiling with epoxy resin grout

[GAZlaunt]

Hi guys got a job coming up soon which ive not come across before its a bathroom I've already started large bathroom marble tiles all around wall/floors which was fine but now the client wants me to tile a paper faced mosaic piece on her large shower wall , the wall has two niches built into the wall and two showers with at least 8 holes needed to cut out for the various outlets, im concerned as I've never attempted to do this before ive never used epoxy grout before and the mosaic piece costs £5.5 k I'm a very competent tiler but would rather ask for help and advice from fellow pros than go out and make mistakes that could have been avoided.
any advice will be readily welcomed, cheers, Gaz.