My wife and I had same the questions a lilttle over a year ago when we went to the 101 Class. If you've already got a stiff leather or webbing type belt, you might want to use that for now. If you decide on what type of eqpt you want later, you'll probably end up checking out the CR or DAA comp belts. As for mag pouches, I prefer doubles, it comes out cheaper since you need pouches for at least 4 mags (the 5th will be in the gun after you load and make ready). Some guys prefer all single pouches, it allows for more space between the pouches. The cheaper, ones are okay, just make sure your mags will fit (I don't know if XD mags are drastically different).
As for holsters, you might want to consider getting one that is made for your make of pistol. Most Production shooters tend to use Kydex type holsters, the ones that are specifically made seem to fit better. Nothing wrong with the cheaper universal types, (Uncle Mike's comes to mind), I've just found that with those types, the tension screw tends to tighten on one spot, while lifting on another. The last thing you want is for some part of you holster to enter the trigger guard when you're holstering.
My wife and I ordered online, not too much cheaper but more choices. We went with Comp-Tac for our M&Ps (excellent but pricey), and I recently picked up one of the cheaper BladeTechs for Single stack. We've ordered with no issues from Comp-Tac(excellent products/customer service), Dillon (fairly cheap), and Dawson Precision(good prices). As far as local, the OGC guys shoot a lot of the matches, you might want to see if they bring in gear. A couple of the guys at Security also shoot, they bring in gear but its not always in stock.