Hi, Stephanie. I've heard of people leaving M&P soap out to "cure" for a couple of days, but I never really understood why. I always wrapped my M&P soaps in plastic wrap as soon as possible so that they wouldn't develop glycerin dew and get all sweaty.
As far as adding things to M&P, I think no more than a total of 1 Tbsp of additives per pound of base is a good guideline. I don't usually add things to my M&P base, but I have added 1 tsp of honey and/or ground oatmeal per pound of base before and it worked out nicely. Adding too much to your bases can lead to either sticky soap (especially in the case of honey) or a decrease in lather. I wouldn't add fresh fruits, veggies or milk to M&P bases because they could spoil and mold.
