A spin off out the now rapidly becoming epic Spingfield SA-35 thread.
Clearly we are about to experience a Renaissance of Grande Puissance and I felt we should build a thread with the same élan as The Art and Science of Keeping Your 1911 Running.
I, personally, know far less about the Hi-Power, having owned a single example in my life. But so far I can provide this piece of advice: Don't insert the recoil spring guide upside down and subsequently rack the slide, because you WILL crush the absolute fuck out of it.
Which brings me to my second piece of advice, you probably want a couple of spare recoil spring guides in your parts kit. Because it is very easy to do the above...
Otherwise, my only other tip is that I've found some sharp edges in slide releases that can cut you if you uses a thumbs-forward grip. So maybe stone those out.
I know Barsto makes semi-fit and match grade barrels for 9mm and .40 and a 9mm conversion for .40 frames. They do not recommend their .40 barrel be installed in 9mm guns. Something about, "Only do this if you want a two (or more) piece frame."