As landarc stated competition and catering are totally different animals with a few similarities. I would not suggest trying to do both to start out with.
Competition is more of a hobby and does not necessarily generate an income for most of those that compete. If you have the money and time you can go this route and you will learn a great deal that will help when you decide to start catering. Depending on how serious you are about competition you could spend as much as you would starting a catering business. But if you just use it to "get your feet wet" you can spend much less and still gain valuable experience.
Catering is a business. A business is for profit. If you decide to start out this way be sure to do your due diligence with both the business and the cooking aspects. Work up a detailed business plan including equipment costs, labor costs, licensing/insurance costs, lease costs, utilities costs, etc, etc. Research, Research, Research. If you have limited capital you will need to investigate financing sources. Find some way to learn to cook an exceptional product. Participating in competitions can help with this or try to find someone local that can tutor you in the fine points of BBQ.
Realistically speaking you are looking at 6 months to a years worth of preparation to be ready and competent to start up a catering business. I don't mean to discourage you but it will take time to learn all the aspects you need to in order to make your venture a success.
This forum can be an invaluable resource to you as well. There is a plethora of knowledge here from Competitors to Caterers to Restauranteurs that will assist you if you ask for advice/suggestion/help. I consider this forum my Number One resource at this point when it comes to BBQ knowledge.
The devil is in the details in any venture. Don't let those details discourage you or detract from your dream. Just remember to have fun on your journey.