Back to the question the OP asked about. As
@djtaso mentioned, using a controller has NOTHING to do with the size of your audience. A controller is just another tool to manipulate the music (in very basic terms). It can, in some cases, give you more options than whatever DJ software you are currently using on your laptop, and basically gives you better/easier shortcuts and visuals for that. One of the best wedding DJ's I know does not use a controller at all. He uses his laptop, an external mixer, mics, speakers, and lights. I will say, he does mainly weddings along with a few private events throughout the year. He's not a "club style" dj. He can transition as good as I've heard anyone. It's what he has always done and he's good at it.
Do you need a controller? No. Could it be a good addition to your arsenal and a lot of fun? Most definitely. Whatever you choose, controller or not, practicing with what you have is what's important.