You will need 25 rounds per stage X 8 will equal 200 rounds WITHOUT ANY MISSES!
There are 5 targets per string X 5 strings per stage (25) rounds
As to equipment wait and see what the other competitors are using and ask questions. 2 magazines should get you through each stage
NRA Life Member, NRA Range Safety Officer, IDPA Safety Officer
As you are, I once was, As I am, You will be.