Help with electrical plan. What's right, wrong, suggestions?
Assuming that the S's represent switches to control the lights, here are my thoughts...


Generally, you do not want your lighting on the same circuit as outlets in the same room. That way if you trip a breaker with a plugged in device, your lights don't go out. This is especially helpful when trying to do the wiring itself because if the outlets and lights are on separate circuits, then you can have the overhead lights on while you are wiring the outlets, and you can plug in lights while you are wiring the overhead lights.

If you don't have a nearby lighting circuit available, you will either have to add one to your breaker panel, or you will have to get approval from your electrical inspector or local code authority to use the existing outlet circuit.

The new best practice is that the power for lights enters the box with the switch, then it goes to the lights. (And in some places, this is code.) It's not clear from your diagram if that is what you intend to do.
From your diagram, it's not clear that you understand how 3-way and 4-way switched lighting circuits work. See http://en.wikipedia.org/wiki/Multiway_switching#More_than_two_locations or consult a professional.
For stairs, you must be able to turn on the ceiling lights from both the top and the bottom. I can't tell from your diagram if you plan on doing this, or if the existing lighting already does this. Since you're messing with the lighting in the area, the electrical inspector may insist on this, even if you aren't actually touching that lighting.