Continuing from part 1 of Andy's Handy Hints
A church is often the cheapest place and not a bad acoustic either. Pay attention to the average attendance and think about downsizing if necessary. Some friends of mine, the group Flute Alors! Have been performing in a hall that seats about 80. Not exactly huge, but it always looks well-attended.
What kind of service will you provide for the community. Make all of your goals clear and give timelines for specific projects you have in mind.
Once a few concerts have been performed and your group is energised about the future, find three well-connected supporters who will herald your successes to the community. Speak to them about your plans and, if they show excitement, ask them if they might be interested in taking a leadership role with the ensemble (I.e. joining a board of governors). You'll need a president, secretary, and treasurer. The treasurer will be extremely important and helpful in future grant-writing. Make clear the purpose of the board from the beginning in order to avoid any stress later.
A charitable organisation has 501(c)3 status in the States. This is very important as it opens your group up to more granting agencies as well as allowing you to issue tax-deductible receipts to donors.