I shoot IDPA up at S&W in Springfield, MA. I think I'm going up there tomorrow night, too
Also, at New England Outfitters in Wallingford, they are supposed to have IDPA 1st and 3rd mondays of each month, but call first. I went, and the guys cancelled it, so I just shot at the range for an hour
As for the other stuff. HK P7 should be fine, I use a glock because its the only gun i have
Most of the people at the S&W use a glock, some use revolvers, some 1911's, and some S&W, and a few sigs here and there. I have an uncle mikes kydex belt holster, and a double mag case. For conceal, i use a light jacket, or a long tshirt now that i have an IWB holster from DeSantis
I have 4 10 rd mags, and a high cap for the start, so i can put 11 in and just rack slide and have the full 10+1. you def want 4 mags at least. I also bought a surefire Z2 for the dark stages they have, went to hoffmans sale, 10% off everything!!!
Def need eyes and ears, and at S&W, you need a hat, usually baseball due to the low ceiling.