Galco offers many holsters for the USPc - www.usgalco.com.

As far as ammo...for defense, any of the modern premium loads from a reputable manufacturer will work fine. Pick one, forget about ammo selection, and shoot a lot.

My USP Compact fits my Hi Noon holster for my FNP 9M just fine.
I buy 357 Sig in bulk from Ammo Man. Georgia Arms has good prices also.
LD

I just recently purchased a USPc .357 sig also. I'm using the 125 FMJ from Wally world. I just made a bulk purchase from ammunitiontogo (500 rounds 125 gr FMJ) for $169.00. I'm going to give that ammo (Speer Lawman) a try. For home defense I use Corbon DPX. Very nice!

Oh yeah and i have a custom IWB holster being made by AKJ Concealco. Here's the link. I purchased 3 of his holsters for my fav carry pistols.

http://www.concealco.com/

You should be happy with Speer Lawman ammo, it has been my preference for range for years and Gold Dot for SD. I don't shoot it exclusively however, I agree with Mike's statement because I have found it to be true but if somebody asked me to suggest a brand I would say Speer.

Congrats on the H&K purchase mnhntr! i have a .357/.40 the .357sig is a hot round you'll love it, today i went to the range and felt like destroying some of my old plinking steel spinning targets so i shot one with the .40 and it folded it up to about a 45% angle and with the .357 it ripped it in half, was a lot of fun. Good Luck!!