I've been to a half dozen signing events in the last year. The most successful one was the FCF launch where I unloaded 155 paperbacks. The least successful one was at a farmers' market on the hottest day of the year when I sold 2 books. Everything else was in between. What I've found is that bookstores don't really want authors. Our local, neighborhood indie bookstore, in spite of being touted in our local, neighborhood paper for their "outreach" with local authors, actually told me, "Authors aren't a big draw". (I guess people only go to bookstores for the coffee these days.) Unless you've been on television or you have some crazy gimmick or you can bring someone famous with you, bookstores are not author-friendly. Some have restrictions on signings based on your book's return status. Others want a larger percent of the sales than either you or the publisher get which doesn't make it worth doing for anyone except the bookstore. Because of all of this, I've actually avoided bookstores which is kind of sad. However, I've found plenty of other opportunities to have signing "events".
Events are a mixed bag, but what I can absolutely tell you for sure is unless you are throwing a launch party and you've already got a known quantity of RSVPs, you don't need that many books. At this point I wouldn't bring more than 20 books to any signing event. Bring lots of bookmarks and swag though because 9 out of 10 people who stop to check out your book ask, "Is this available for Kindle/Nook?" As my husband said at my last event, if they don't buy it here today, you want them to buy it somewhere, so send them on their way with a bookmark and assurances that the book is also available as an ebook. (I unload a LOT of swag at events.)
What I can also say, and this is something I've heard from a lot of authors, is don't say no. Unless it is massively inconvenient for you and costly, don't say no to any opportunity offered. Especially if you're just starting. You never know what kinds of other opportunities will arise from going to things that seem to have no value at all. Even if you don't sell any books, connecting with potential readers, reviewers and other authors is always worth it. I have not said no to anything this past year except for one or two things where I was ill or I had a family obligation that could not be set aside, and I've always, always, always come away with another opportunity.