You probably have the gear for IDPA right now. It is the least 'gear intensive' sport. USPSA/IPSC in single stack would be next, but you might not have enough mags or mag pouches. You should shoot with what you have for a bit before you make any major gear purchases.
3-gun is a different world, and the gear requirements are much greater. Start with IDPA or USPSA (whatever you have locally). If it lights your fire, then get into 3-gun.