The shelves.... We originally wanted a 30" x 12" niche but when we opened up the wall, there was a septic vent smack in the middle. We decided on 2 niches instead, I wassn't about to mess around with those pipes. When figuring the tile layout for the design I wanted, our friend suggested that we oversize the niches so the tile would lay out nice - he suggested 18 x 18 niches and I freaked. But the 12x12 would not have been big enough for the 3 kids and all their stuff. He suggested a granite shelf on the bottom and then one above it to make a shelf for soap, razors, etc. We talked about the length and width of the shelves, but never the depth. When I picked up the shelves from the granite fabricator, I freaked - they were 1 1/4" thick just like the countertop was being made. Friend said, don't worry, they would be perfect. They are. I honestly wouldn't want them any thinner. When he laid the tile, the bottom shelf slid in tightly and then he cut the bullnose on the side and the back tiles so the top granite shelf sits on the cut tiles all around. The tiles abouve the top shelf are full 6 x 6 and as you can see, we have enough height for those huge oversized shampoo and conditioner bottles. There is kerdi behind so no worries about water issues and they were all caulked and all afterwards. Being the over-emotional one, I figured this design that had been in head my for 2 years was ruined when I saw how thick those shelves were, but I wouldn't want them any different. I think they 'fit' the design perfectly as is. And I just love the niches. Before, the kids had a tiny corner shelf and bottles were all over the place, now there is enough room for everything plus space for guests when they are here.

Install "old work" round boxes where you want the lights to be. Run the existing wiring to one of those boxes instead - (the existing wire had better reach one of them!), since you're you're going to be eliminating/patching the original box. To get the wire to reach, you may have to deal with loosening a wire that's secured (stapled) in the wall to the stud. Pull addl. wire from the first box to the second box (drill stud carefully). Repair wall, install lights. If you're dealing with older style wiring, or you feel you're in over your head, hire a professional. Consider it an investment in safety.

The "regular" bath layout that jensbride posted first is very similar to what our DD & DS shared for years and worked very well. The door, however, was a pocket style and placed directly across from the toilet. This allowed the vanity to be scooted around the corner to take up the whole wall. It leaves the toilet close to the tub, but with lots of elbow room. Our kids just learned to keep the door partially closed when the bath wasn't in use due to the "view".

If you leave the layout as is, do one sink. Having counter space in a bathroom is important. When we did our remodel several years ago we opted to put in one big sink with two faucets in our kids bathroom. I'd never done a remodel before (we did the whole house) and with so many details to consider/decide upon, it never occurred to me to check how much counter space there would be vs doing a smaller sink with one faucet. Big mistake. There is not enough counter space.