Izzy, I was in your position one time, and the wig store turned out to be a VERY pleasant experience. It turns out that I wasn't the first pre-trans MTF that they had seen. They showed me wig care, including how to brush it and clean it. All in all, it gave me confidence enough that going out as a woman the first time was FAR easier.
Now, that being said, I went into another one before I found this one and was promptly "run out" by the proprietor. You might want to CALL the wig store in question and explain that you're transgender. Check out their reaction. If they're negative or neutral, you may have to find another one.