As said, your SR1911 will be just about perfect for IDPA CDP.
You need the gun, at least three magazines, a holster, magazine carrier(s) for two, a good stout belt, a concealment garment*, and eye/ear protection.
You will not be required to fire more than 18 shots on any one string of fire.
A typical match will be maybe a hundred rounds, but take extra.
*The concealment garment can be about any sort of jacket, vest, or long shirt. I strongly suggest you practice clearing concealment to draw DRYFIRE at home before having to do it under match pressure with a loaded gun.
The new shooter's briefing has a lot of good information and is easier to get your head around than the rule book:
http://www.gadpa.com/index.php/idpa/...oter-briefing/