With no windows, see if you can put in solar tubes. The natural light really makes a difference in how the space feels. You can get them with an integrated light or vent fan.

If you're trying to make the space look larger /brighter, forget dinky little rectangular mirrors over the sink(s) ... and go with a large 10' mirror to top the whole vanity. Frame it so it doesn't look "builder basic". I think you're describing an alcove for the vanity, and that works well with a large mirror ... whereas it will look overly "busy" with trendy rectangular mirrors.

Go with pendant lights in front of the mirror, but put them on dimmers (because lights in front of a mirror will "double" their light).

Solar tubes are a good idea, but nature will always fight you 24/7 any time you put a hole in your roof.

@theresa, I love that idea and to be honest, in my last bathroom we had a huge rectangle with no frame because I like super minimalist/midcentury, because it was mounted on a painted brick wall so the wall had enough interest. This one will be on a brick wall as well but I had the wall built to handle two mirrors (the junction boxes are in place), which is why I was trying to go as large as possible with them.