1. Do on-line searches for professional labs. Avoid those that advertise specials and offer a free photo mug with every 100 4x6 prints. They're going to be geared toward consumers. Once you have a list of a few candidates, look for on-line reviews. I would also check out local camera clubs; they're almost guaranteed to have someone who is a printing fanatic (every club does).
2. Ask the the store owner how much space you can have, and how many pictures she is interested in. Remember that less is more, and 2-3 larger images with lots of space between them will display (and likely sell) MUCH better than a bunch of 8x10s jammed together. I would suggest that 11x14 and 16x20 are good sizes to consider; small enough to not require a huge amount of wall space, nor be a major commitment, but large enough to have some visual impact.
3. I would avoid mats and frames altogether. Gallery wraps, float wraps and aluminum prints are very popular and have the benefit of not needing to match the decor as frames and mats do.
4. A discreet ,hand-written signature is fine. I have a high-quality "gold" ink artists pen (~$10 at Michael's or artist's supply stores) that I use. DO NOT include a digital water-mark, etc in the print.
5. Pricing works however you need it work. Since you don't really have any overhead, you have a lot of flexibility, but remember that price adds to the perception of value; in art, higher prices (not crazy-high) will often sell before lower ones because of the perception of value that it imparts. I would say go for 4x the total cost and let the owner know that there's some "wiggle room" in the price.