The 51 st suggests a private home, as this will exclude intrusive people and noises. You should announce your purpose for forming the group, introduce the command staff, state your general principles, goals and by-laws, and finish within an hour. Keep it short and simple and do not allow it to become a public forum for gripes. You can then weed out those who do not wish to go any further with their involvement and at the next meeting begin with your agenda. All meetings should be open to the public and in a public place.
Libraries are great places to meet because they are free to the public.
Be sure to reserve the meeting place in advance of each meeting. You invite the public. You specifically do not have to invite the press or local law enforcement, but keep the meetings open to include them if they wish to attend. If you do not make you meetings public, you will make yourself a target of criticism or more. It's hard to get new people interested if you don't advertise who you are, and when and where you meet.