When I did my shower I used 12" tiles in a 3' x 4' shower. I have a window in there too, so I knew before hand I would have tons of cuts so I chose a porcelain tile with the clay the same color as the surface so cuts would be less noticeable. At this point, your best bet is to be extremely careful with your cuts so there is no chipping.
Then I used a smoothing stone like this to clean up the cut edges:
Finally, if at all possible, position the cuts away from view. IOW, any cuts that will be above eye level, put the cut edge up. Any cuts below eye level, put the cut edge down. In the niche, put the cut edges along the back rather than front.
Like cleveman said, caulk any change of plane. Some people use silicone caulk. Personally I would choose a caulk that matches the grout.
Edited to add: If you are not happy with the cut tiles, you might play around with using those mosaic accent tiles around the niche too.