I wouldn't try a polish version on my phone until a North American carrier drops an update - then watch XDA for custom ROMs. Speaking of which, Samsungs (from what I've read) pretty much have to be based off the stock ROM, unlike my old Galaxy Nexus where everything was based off pure AOSP (Android Open Source Project). It made for much cleaner ROMs.
As for XDA - don't just grab any ROM, do some reading and research. Find out who the reputable developers are and use those, and only from a trusted download site. If anything seems fishy, bail out. I was going to ROM by old S4 - hoping for a more "pure google" experience, but it's a lot more involved then it was on my (really old) Gnex, so I just left it.
Your best friend is time spent doing research. And coffee - because life is just better with coffee!