With a venue in mind, an insurance provider on the line and a band ready to book, you've got one more piece of business to look into before signing on the dotted line: scheduling conflicts.
If there's another event happening on the same day as your show, and that event is appealing to a similar target audience, you're going to have more trouble selling tickets than you need to. Before solidifying a date, check all local-entertainment calendars, concert venues and bars to find out if there are any same-genre concerts happening on the same night -- or even the same weekend. People will be quicker to buy your tickets if they don't have anything else going on in that immediate time frame.
If you find a conflict, just pick a new date -- and then do another search for conflicts.
Next, once you know your date, you may need to tell the city.