<p>I too would like to ask you to keep it simple, and if you can tell us where this will take place, it will help to get more focused great advice. A few points to fill the gap of information that you have already received:</p>
<p>No new lens needed, even the kit lens is sharp enough, but the focal length is important as you need to allow everyone to fill the frame without leaving people at the edges to look distorted, which happens when too wide a lens is used and when shooting too close to the subject. Indeed 30mm sounds about right but you still need to look in the VF to make adjustments. You may want to leave some room on the edges, which can be later cropped out, and do not put ladies there who will be very upset if their bodies look wider than normal.</p>
<p>If you have several rows of people, you may run into problems of not enough depth of field — some rows are in focus while others are not. You can fix this by changing the arrangement of the people, using a smaller aperture (high f number), and/or pointing the focus slight behind the very front row. You need to experiment. Another option is to have the camera set up higher than the group so it is shooting down, which flattens the filed and reduces the depth. You may or may like this look, though.</p>
<p>Buy a remote (ML?, can't remember) and set your camera such that after you press the remote, it will take 2 sec before it triggers the shutter. In this way you do not have to run from the camera to where you are in the group, and will not get caught with your hand holding the remote. You trigger the shutter and quickly put the hand down to hide it.</p>
<p>A good tripod is definitively needed for this and for any other general group pictures. If you are semi-serious with photography, get a carbon-fiber version rated to hold the heaviest camera+lens that you have now and may own in the near future. The lighter it is, carbon fibers are both strong and light, the more likely you will use it often.</p>
<p>If you are shooting indoors and there is no direct sun light, a good flash plus a diffuser seems inevitable, which will add to the list of things you need to buy.</p>
<p>(Hope you are still planning to do this and not going to quit …)</p>