Ignore the following if your goal in firearms ownership is to have a collection that you can post pics of on the internet and get the other inter-dweebs jealous.
If you're interested in owning tools not collector elvis plates, read on.
I used to be headed down the path of piles and piles of useless metal, wood, and plastic cluttering up the place.
My advice is to find a platform that works well for you, both handgun and rifle, and stick to it. For me it's the 1911 and the AR platform. I'm selling or have sold off everything else. I have .22 caliber conversions for both so I can plink, be really quiet (suppressor on order), or teach newbies.
I also got tired of having a bunch of different calibers cluttering up the place. I'm sticking with .45, 5.56 and .22 LR for now. Eventually I might get back into .308 with an AR10 or two. I also may get a Colt Mustang in .380 for a deep concealment gun.
If the HK USP platform works for you then I'd stick with that. The biggest problem I see with doing that is that I don't know of any .22 conversions for it. The nice thing about a .22 conversion is that even when you're plinking you're still training in terms of sight picture and trigger control.
Go compete and get training. It will quickly expose the weakness of owning many different platforms.