Sounds exactly like my guest bath, and you need three.

Three is not overkill. We have a 5'x5' guest bath with a 28" vanity, no windows. Our three light fixture, above the vanity, is the only light source is the right amount to my eyes. You can always change the bulbs down if you think it is too bright.

I would go with 3 pointing down. As you get older you need better lighting. With long vanities like they are putting master baths I would go with 6. That is what I ordered in this house but they thought they knew best and put in 2... 3 light fixtures over the sinks. I do make up and hair in the middle of the vanity and my light is not good.

Thanks everyone. I'll stick with my original 3 blub fixture and start out with 60w bulbs instead of the 100w max. May be forced to put CFLs in there due to the heat (sigh)