Peace Lily flowers rarely last longer than a week or two, so their demise does not mean your plant is unhappy. Cut off the flower stems as soon as the flowers start to fade.
Your watering is probably about right. Ideally, you should water a Peace Lily just as or before it starts to wilt. An occasional wilt from dryness will not harm the plant. Water it really thoroughly and then see how long it goes before it starts to wilt. That will tell you how often it needs water. This is a plant that doesn't tolerate dry soil, although it can be overwatered.
Very bright light that avoids the rays of the sun falling directly on the leaves is best. Peace Lilies also do well under just office fluorescent lights if the lights are on for at least 8 hours every workday.
Monthly fertilizer at half strength will help promote flowering,
Unless the AC is very close to and blowing directly on the foliage, it should not be a problem. Misting will not help with either the AC or low humidity. Do it if it makes you feel better, otherwise, don't bother.