I think you could leave the threshold unless you have to change it. how has the shower been waterproofed?
yes, the two tiles you've picked out look great together. I would still do the gray grout,,,maybe Mapei silver or pearl gray. yes to that same basketweave for the niche.
make sure you find out if those gray subway tiles come in bullnose for your edges. find out how he's going to do the niche FIRST. I've seen some horrible niches done w/subway tile because they don't properly measure and/or do the bullnose edging.
If these tiles come in a long/bigger size, get those.
your tile guy should really plan out the size of the niche in relation to subway tile placement. you don't want little slivers or a lot of cuts. the niche should fit perfectly within the tile layout. make sure you know how high you want it, and try and place it out of the way of the shower spray. I was super picky about mine and made sure I didn't get any small cuts. The bigger one was visible for the dispensers, and the little one down low is for stuff you don't want to see.
you prob want a taller one for your shampoo, and a short one below it for soap/razors.this one is edged w/bull nose tiles. you do not want the sides of the unfitted tiles to show. if there is no bullnose, get a Schluter edge (like I did w/mine. the black metal one) . below, bullnose tiles. glass shelving. notice,,no small cuts around the outside edge of the niche. this was good planning by the tile setter.
compare to this one below. see the tile cuts on the top part of the niches? There isn't one on the bottom part so it looks asymmetrical.
this one, below, is ok. would have been better if it didn't have the small cuts on the right side, both in and out of the niche. Remember,,what ever is on one side should be on the other. If he had widened this box by a few inches, it would have been better.
this box below has the exact cuts all the way around the box. look at how well the lines all line up too. Good layout.
this one below is a NO
btw,,,when he lays the sheets on the floor, make sure he staggers them so you don't get a grid effect.
Q
niche tiling, grout etc
Q