"... How many would be the next question..." And the answer is...wait for it..."it depends!" :-) Depends on so many things, beginning with the design and type of sconce: is the light throw down, up, sideways or all of the above, or none of the above. There are many, many kinds of sconces, just as with any other type of fixture. At the end of the day, one is left with a question or two: 1) Am I concerned about lighting something(s) specific, and; 2) Do I care if the fixture is visible, and/or is an "eye magnet"? The answers to these questions will tend to answer "how many?" :-)

I would add a can light in the ceiling...it looks like your plan already specifies that. It's the circle with cross next to your toilet. Good idea to switch locations of toilet and sink...you don't want to be staring at the toilet as you walk in. I would do a can light above the toilet. EDIT: Errr...sorry it's the exhaust vent. I would do the exhaust vent over the toilet. With a can light in front of the toilet.

Wow ... that is one ugly light fixture in what looks like a cool, hip, sophisticated apartment! Looks like something you might find in a powder room. I'd remove the fixtures entirely, cap off the electrical wires temporarily and try to hang something (piece of art? textile?) over the mounting bracket. Is that even a possibility?

I agree with ACM, just wanted to say that you win 10 points for spelling them "sconces" in your title. I have seen "scones" far too often lately! Can you move both of the sconces so they are balanced and the one is just past the plumbing pipe? I have also seen them placed on side walls in front of a wall-to-wall mirror, though that looks odd to me, it is not as odd as one near the vanity and one near the toilet.