Depending on the mesh, realize that mounting tile like that on a vertical surface ramps up the challenge of installing them in a big hurry. Gravity is fighting you. You will spend considerable time hanging and manipulating the sheets/pieces. Ideally, you want to hold the top of the sheets and hang the sheet a little high on the wall (maybe 1/8”), then press it into the setting material lightly, then pull the tile from the bottom row down to ensure to sheet is spread out fully (by using a clean margin trowel in the bottom grout joint) to its final proper location…then embed the sheet to the setting material.
Mastic can cause bleeding/staining problems for all sorts of natural stone. If you want to use mastic, pick one that
explicitly states compatibility with natural stone. Realize that mastic does an unintended job of softening some paints up pretty good. I’ve removed a tile held with mastic after 45 minutes and it took the entire layer of paint with it. This softening isn’t horrible…you just need to be aware of it. Once the stuff dries out, the paint hardens back up and everything sticks fine.
For me, I’d pick a good non-sag mortar. It’s plenty sticky and it’s easier to clean if some gets onto the front of that tile.
Using epoxy over that tile is kind of pointless. Why spend all the extra hassle and expense for epoxy grout that takes up a minority of the surface when the majority of the surface remains fairly stainable? Sure, you can seal the tile, but sealing isn’t a process that puts a protective layer on the tile….rather, typical penetrating sealers try to clog the surface pores so that stainable liquids take a little longer before they soak in, giving you a few minutes to clean before they become permanent. And I can tell you that you’re likely to use a lot more epoxy grout than you think $$$$.
I’d be much more apt to use a grout release, use Laticrete Permacolor grout (that dries to the advertised color), then seal everything with a superior sealing like DryTreat.
But before I did anything, I would spend a little money making up a test board and grouting it. You really want to know what that’ll look like before being surprised at the end of a finished job. I can’t stress this enough.