There's some great info here!
As someone in this thread recommended, it's probably in your best interest to see if you can shoot a couple of the most popular options, Glock CZ75, 1911, etc. People have some strong preferences for how they feel. This is my first year in IPSC with my first shoot in a couple days; I'm going to be shooting classic as I have a 1911 I'm very happy with... But on the flip side, I bought a Glock 10mm and be damned if I'm not very accurate with it without any practice, somehow. If you find you shoot better with one, it might be worth starting out in that direction. The only word of warning - Glocks are typically very similar to one another, the CZs see minimal changes as their fame is in the unmodified production division, but the 1911s vary wildly from the vulnerable Norinco (which people have had great success with customizing) up to high-dollar Infinity raceguns. In a nutshell... not all 1911s are the same.
I dont know that there is a division that suits newcomers best. Your division will likely be decided for you by what firearm you choose. The Open division will see the harshest competition, you'd be more confident to steer clear of that, for now.
Finally, also as a newcomer... I received a tremendous amount of information in my Black Badge course. I would see if you could track down some formal handgun shooting instruction BEFORE you take your Black Badge. They'll be able to set you up with shooting fundamentals that you can build on as you work your way up.
I shouldn't comment on holsters/mag pouches, etc yet. I have spent a lot of money experimenting already; I finally decided to quit wasting funds and just go give it a try. I'll keep you posted.
Good luck!