You will need to complete the water proofing before anything. I do not think the pebbles go with the tile choice at all.I would choose a solid color tile in a color from the floor in porcealain 12 x24 and the same color in a smaller tile for the shower floor. The tile you have would be best horizontal since the striations are vertical and will drive you crazy if they don’t line up.

I was going to retire our master bath and lived the idea of the pebbles. My neighbor had installed pebble tile in her shower four or five years earlier, so I asked to see the results. How disappointing! There was lots more grout than I had expected, necessary to fill the spaces and level the floor. In addition, the excessive amount of grout made it difficult to clean the floor evenly. My neighbor had a cleaning woman at least once a week and I know her to be meticulous, so I knew the pebbles were not for me. If you still want pebbles, ask to see some with the grout applied so you know what you are getting.

I would do a running bond horizontal. The striations, IMO, pretty much lock you into horizontal, as Patricia Colwell Consultingsays.

I would also consider ditching the pebbles and going with the mosaic that matches the wall tile. the cohesive design element will be calming. And - I also worry about how the pebbles actually feel and hitting it wrong with my heal and it being ouch-y if the grout is at all recessed. ALSO - I HATE seeing the edges of the sheets or a grid pattern on a floor. Drives me insane. Figure that's much more likely with pebbles than a square or rectangular shape.

And - FOCUS ON WATERPROOFING - the best / most gorgeous tile in the world won't protect you against water damage from poor prep

I would use a bright, clean looking white porcelain tile in the whole shower. The white will match your vanity cabinet and baseboard trim.

Between your countertop and floor tile, you don't really want to introduce another faux-stone look.