While it can depend on the overall style of the room, as a generic statement I'd say that I wouldn't have one tile pattern meet another pattern straight on with no transition between the two. That's for most people and most installations. I think what you have to do is look at a lot of online photos. Or do mock up with your materials on hand. You may not be able to verbalize what you like, but when your eye sees it, your brain will give a "yea" or "nay" vote, and that'll help you define your style. Stye-wise...if you were going for a minimalist design? Simple? Clean lines? Minimal visual distractions? Then having one pattern butt right up to the other can look just fine. But the two tiles should relate to one another in some manner: Pattern, shape, size, color, texture, material, etc, etc. Some folk find pattern-abutting-pattern pleasing. But it depends on the tile, the pattern, etc. Others find it jarring. For a more traditional design, having a border or transition of some sort between them may be the better way to go. For a border or transition? If your shower wall was, say a marble subway. I'd terminate that pattern at the edge of the tub with a vertical run of tile. For a less busy look the tile for the vertical border could be the same used in the shower. If you want to blend details, it could be a darker tile, or something for example you used as an accent elsewhere in the shower, perhaps the same tile you used on the back walls of the niche. Easiest and safest is to use the same material as the shower tile. The vertical of the border will act as a transition between the marble in the shower and the backsplash pattern on the sink wall. In the end, trust your eyes and your gut. If it feels wrong, it probably is wrong. For you. Good luck.

You would definitely need to get a smaller mirror to have more space, but I see many issues with your space when comparing it to your inspiration. Where will you end the backsplash on the right side? Does the left side have a wall as a natural ending? Honestly, I agree that a four inch corian backsplash is the way to go here.

I have a wall-mounted sink in a powder room which gets a lot of use from 2 kids. No backsplash. Funny, it was fine after I painted and caulked it years ago, but since we had "professionals" redo it 18 months ago, I'm thinking about installing a backsplash. The muddy splashes clean off well enough but the wall-sink interface is not doing well at all. I do think a quality paint job should be fine--wipe it down and you're good. Caulking the crack properly is crucial though. Be aware that small kids will be tempted to stand on that shelf to reach the sink, or just because.

the white trim prob wouldn't be much higher than the granite. (usually 4") So, if you really want higher, you could see about doing some decorative thing to make it higher, but not sure how that's going to look. A good bathroom paint on the wall, and vinyl trim piece with equally good enamel paint, should be impervious to your splashings! (I would have done a wall mount faucet. much easier to keep clean) then you could have had the granite come up about 9-10 inches. or, you could do something like this i would have forgone the wainscot on that wall and just done the tile one last pic w/the wainscot. the trim piece sits a bit higher than the countertop piece. take you pick of what you like.