O.K, let's take one step at a time. Between all of the members on the forum I think that as a community we offer some very good and practical advice. But one thing that we don't know for sure is how good, in practical terms a person is, or, in the case of somebody starting out for the first time, whether they are ready to, or cut out to become a D.J in the first place.
The earlier advice of finding a "Mentor", gives you the advantage that you can experience what being a Mobile D.J involves before actually committing to buying lots of expensive equipment. Starting out (and investing) in the correct equipment is going to cost some $$$'s and in this industry you do need to start out on the correct footing. Basically you need to be sure that D.J'ing is right for you, and you are right for D.J'ing!

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We know very little about your experience, if any, and this is where we need to concentrate any advice!. Have you ever attended Weddings, or Family occasions and watched the D.J and what was involved?. Doing Mobile D.J work is a lot different from Mixing at home or in a club, or doing a School Dance for example.
Are you confident about being able to play all types of music?, and perhaps use a microphone in front of 200+ people?. I don't doubt your enthusiasm, or willingness to learn, but a good D.J and reputation is built from experience and not
just from a forum or a text book!.
I'm not trying to put you down, or say that you are too young to D.J properly. Quite the opposite. Nobody on this forum wants you to go out unprepared or get a bad reputation just purely because you are inexperienced or ill-advised.
Being a Mobile D.J involves some key factors:-
(1) Playing all types of music for all ages, and having a varied music selection. Doing Mobile work involves playing music that you may not choose to listen to in your own time, or have so far even heard of!. Check out the threads on 70's and 80's music for some examples.
(2) Being able to use a Microphone in front of a large number of people.
(3) Appearing approachable, and outgoing and being able to break the ice, and create a positive atmosphere amongst people you have never previously met (Probably the hardest thing to learn!)
(4) Being able to read the dancefloor - again this comes from experience,a nd enables you to see exactly what is working and what isn't music wise!.
(5) Being Reliable - You can't just decide not to attend a function and let somebody down just because you've been invited to a Friends Party or decide to go out clubbing instead!.
Above all, it's very true when you hear other D.J's stating that a D.J can make or break a Function or party. Take a Wedding Reception for example, a Bad or inexperienced D.J could ruin an otherwise perfect day for the Bride and Groom. In the case of Weddings, the memories of their Wedding Reception will be with them for life. So there is some responsibility which attaches itself to the role of a D.J or Entertainer.
If you have read the above, and it is a good description of you, then you are on your way to becoming a D.J. If its put you off, then perhaps you are not ready yet?.
My own advice, is to go ahead and invest in the equipment that you require to do proper functions and mobile work, but do it properly and get the correct equipment right from the start. Instead of perhaps advertising your services, just concentrate on doing functions for children and those of your own age. This way you will be familiar with the music, and it will allow you to gain a little bit of experience and more importantly build your confidence. Perhaps you could ask to do Disco's at your own schools, or the Junior (Elementary?) Schools around your area?.
I still strongly advise you to gain some professional advice and guideance from a "Mentor" D.J before you start attending Weddings and D.J'ing at Adult Functions on your own.
With regard to running it as a business. This is where the experience comes in!. It is very, very difficult to run a Disco as a Sole Income. Many of the full time professionals on this forum, have themselves run it as a hobby for several years. Most people still only D.J as a part time profession. If you do it correctly then being a D.J will possibly give you a good source of income through school and college and you shouldn't use it as an excuse to prevent you from following a career. You may want to D.J full time now, but try and get some good grades to fall back on, in case you lose interest in it as you get older, or it doesn't work out in the way in which you anticipated, since it can be a very difficult and unpredictable industry!.
Okay, if you've not been put off, or fallen asleep by this point, here is some advice on equipment.
I'm assuming that you already have a form of mixer and turntables?. If so you have got the basics to start out. You may decide to buy a Dual CD Player since on the mobile circuit they are far more practical than Turntables. However, if your material is all on vinyl then you'll probably not benefit from the purchase of a CD Player just yet. If you do start getting a lot of gig's then consider flightcasing your turntables and Mixer along with any other audio equipment that you may buy. Flightcasing isn't cheap, but neither is replacing equipment if it gets damaged!.
Audio:- At least 400W to start off with, but if you can afford to go spend more on a slightly bigger system then do so. Although a total of 500W - 800W should be plenty for the average function. Since you've already bought Equipment from Gemini, you could keep the same theme and consider one of their Amp & Speaker combinations. Their "X2" Amplifier and a Pair of "GSM-1500" Speakers would give you a basic P.A. Alternatively a Gemini "X3" Amplifier and a pair of "GT-3002" speakers would give you a higher power system and may be better if you intend to do larger rooms!.
Another Amp was recently recommended by Jorge (cubanpete41) is called a Pyramid PA1800X - information
HERE this is a resonably priced 2x 250W amplifier.
Lighting:-. You will need at least a couple of lighting effects to start off with. Chauvet are very popular effects and manufacture a good range of competively priced units. Their website can be found
HEREIt's difficult to recommend products to members in the U.S since I don't know what is or isn't easily available from distributors over there. But from experience I know that Gemini and Chauvet products are worth looking at. As are JBL P.A Equipment, American D.J, Martin and Abstract products. But it does depend on prices and avilability locally to you.
If you need advice on anything before you buy feel free to ask. In the meantime, asking questions and reading post's is a good way to get at least a basic idea of what being a Mobile D.J involves.