I agree with both other posters to this thread completely. However, I would add this, to be successful in this business today you must be very versatile. If you open a room you must offer something different than the other rooms in your area and state. Before I opened my room, I went to every pool room in the entire state of Washington. I did this to check out what I thought was good and bad, and what I could do to be different. Lets face it, a pool room has to be tailored to the largest economic class of people in your area, along with the type of people you as a business owner want to attract. If you are located in the country, you would most likely need to offer things at different rates than in a large city.
I am located approximately two miles from two Military bases, one Army and One Air Force, and along with this I am also in a Suburb of Tacoma, Washington. The one thing that know one in this State had going for themselves was a one stop Billiard / pool locate. My room has a pro-shop with anywhere from 150 to 200 different cues for sale daily, along with all sizes of cases, and almost any type of Pool / Billiard related accessory. I offer full cue repair, from tip replacement, refinish work, to custom cue building. Currently there is no type of repair I can not accomplish, and the basic repairs are completed while the customer waits, IE, Tip, Shaft cleaning, Wraps, refacing of joints, weight changes, and any other basic repair. I also sell a full line of bottled Beer, along with a wide assortment of soft drinks, snacks, and microwavable food. By only selling beer, I can keep my place all ages, which is very helpful in keeping the tables rented. Kids can be a pain in the ass or a blessing for a pool room owner, and it will depend completely upon the people in charge of running the room. Kids want to be treated with respect like everyone else, if you do it, set rules, and totally enforce them you will have no problems, in fact I have found that most people including our young want a safe place to hang out. Oh and by the way the kids today have a great deal more money to spend than I ever did.
Next, you must take the time to know your customers, including the kids, because once people see that you are interested, they will also feel obligated to act according toward you and your place.
Advertisement, is also very important, however, it can also be very inexpensive if you handle it the wright way. Pool Leagues are great way to advertise, to do this keep to your place safe, keep it clean (especially restrooms), insure that your equipment is perfect repair (including house cues / bridges) and offer special benefits to your league players / Teams and you will have more teams than you can handle. This more than anything else will bring new people into your place on regular basis, and by offering quality repairs / work along with good fair prices on merchandise word of mouth will be a great form of advertisement. Word of mouth advertisement is the best form there is and it is free which also is great.
I hope this helps, good luck with what ever you decide to do!!!!!!!