The Hi-Power is one of my favorite "full-size" semi-autos (the 1911 being the other). I use a Galco IWB holster that is for a 1911 Commander and it fits the Hi-Power perfectly. A loose t-shirt in warm weather, or a jacket or sweatshirt in colder weather cover it up nicely. An excellent choice for concealed carry in my opinion.
Ammo-wise, I stick with 124gr or 147 golden sabres, gold dots, or rangers/pdx1.