I can't add much more to what has already been posted. Shoot whatever it is that you enjoy shooting the most and can do so safely.
The only thing that is the same for me now after 3 or 4 years of shooting IDPA as it was at my first match is the caliber. I started shooting IDPA with my Springfield 1911 then moved to a Glock 21 and now to my current primary competition and carry gun, the M&P45. Any gun will do as long as you will do! Just need to make sure it is in something 9mm or larger, you have a good safe holster and at least 2 magazines (3 or more is preferred) and about 100-150 rounds of ammo. Shoot a few matches, talk to the shooters about what they carry and use and after several matches then you can decide if changing anything about your current set up is needed. My holsters, belt, mag carriers, cover garment, shoes, hearing protection, eye protection...all of that changed after shooting several matches and getting a chance to really see what my gear did properly and what it did poorly. Going cheap on carry gear is a bad idea and while I am competitive I shoot using my carry holster and my every day belt so I know it works in every day situations and in some that I'd probably never find myself in.
Now run, don't walk, to the nearest match and have a good, fun and safe time!